485BPOS

As filed with the Securities and Exchange Commission on November 18, 2013

1933 Act File No. 2-36431

1940 Act File No. 811-2032

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C.  20549

FORM N-1A

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

POST-EFFECTIVE AMENDMENT NO. 56

AND

REGISTRATION STATEMENT

UNDER

THE INVESTMENT COMPANY ACT OF 1940

AMENDMENT NO. 46

MFS® SERIES TRUST XVI

(Exact Name of Registrant as Specified in Charter)

111 Huntington Avenue, Boston, Massachusetts 02199-7618

(Address of Principal Executive Offices)

Registrant’s Telephone Number, including Area Code: 617-954-5000

Susan S. Newton, Massachusetts Financial Services Company,

111 Huntington Avenue, Boston, Massachusetts 02199-7618

(Name and Address of Agent for Service)

APPROXIMATE DATE OF PROPOSED PUBLIC OFFERING:

It is proposed that this filing will become effective (check appropriate box)

x immediately upon filing pursuant to paragraph (b)

o on [date] pursuant to paragraph (b)

o 60 days after filing pursuant to paragraph (a)(i)

o on [date] pursuant to paragraph (a)(i)

o 75 days after filing pursuant to paragraph (a)(ii)

o on [date] pursuant to paragraph (a)(ii) of rule 485.

If appropriate, check the following box:

o this post-effective amendment designates a new effective date for a previously filed post-effective amendment

NOTICE

Notice is hereby given that this Registration Statement has been executed on behalf of the Registrant by an officer of the Registrant as an officer and not individually, and the obligations of or arising out of this Registration Statement are not binding upon any of the Trustees, officers, or shareholders of the Registrant individually, but are binding only upon the assets and property of the Registrant.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all of the requirements for effectiveness of this Registration Statement pursuant to Rule 485(b) under the Securities Act of 1933 and has duly caused this Post-Effective Amendment to the Registration Statement to be signed on its behalf by the undersigned, thereto duly authorized, in the City of Boston and The Commonwealth of Massachusetts on the 18th November, 2013.

MFS® SERIES TRUST XVI
By:	JOHN M. CORCORAN*
Name:	John M. Corcoran
Title:	President

Pursuant to the requirements of the Securities Act of 1933, this Post-Effective Amendment to its Registration Statement has been signed below by the following persons in the capacities indicated on November 18, 2013.

SIGNATURE	TITLE
JOHN M. CORCORAN*	President (Principal Executive Officer)
John M. Corcoran
DAVID L. DILORENZO*	Principal Financial and Accounting Officer
David L. DiLorenzo
ROBERT E. BUTLER*	Trustee
Robert E. Butler
MAUREEN R. GOLDFARB*	Trustee
Maureen R. Goldfarb
DAVID H. GUNNING*	Trustee
David H. Gunning

WILLIAM R. GUTOW*	Trustee
William R. Gutow
MICHAEL HEGARTY*	Trustee
Michael Hegarty
JOHN P. KAVANAUGH*	Trustee
John P. Kavanaugh
ROBERT J. MANNING*	Trustee
Robert J. Manning
J. DALE SHERRATT*	Trustee
J. Dale Sherratt
LAURIE J. THOMSEN*	Trustee
Laurie J. Thomsen
ROBERT W. UEK*	Trustee
Robert W. Uek

*By:	SUSAN S. NEWTON
Name:	Susan S. Newton
	as Attorney-in-fact
Executed by Susan S. Newton on behalf of those indicated pursuant to a Power of Attorney, dated September 11, 2012 (Trustees), and a Power of Attorney, dated September 11, 2012 (Corcoran) (DiLorenzo); filed herewith.

MFS Series Trust I

MFS Series Trust II

MFS Series Trust III

MFS Series Trust IV

MFS Series Trust V

MFS Series Trust VI

MFS Series Trust VII

MFS Series Trust VIII

MFS Series Trust IX

MFS Series Trust X

MFS Series Trust XI

MFS Series Trust XII

MFS Series Trust XIII

MFS Series Trust XIV

MFS Series Trust XV

MFS Series Trust XVI

Massachusetts Investors Growth Stock Fund

Massachusetts Investors Trust

MFS Institutional Trust

MFS Municipal Series Trust

MFS Variable Insurance Trust

MFS Variable Insurance Trust II

MFS Variable Insurance Trust III

MFS California Municipal Fund

MFS Charter Income Trust

MFS Government Markets Income Trust

MFS High Income Municipal Trust

MFS High Yield Municipal Trust

MFS InterMarket Income Trust I

MFS Intermediate High Income Fund

MFS Intermediate Income Trust

MFS Investment Grade Municipal Trust

MFS Multimarket Income Trust

MFS Municipal Income Trust

MFS Special Value Trust

(each a “Registrant”)

POWER OF ATTORNEY

The undersigned, a Trustee of each of the above-mentioned Registrants, hereby severally constitutes and appoints Mark N. Polebaum, Susan S. Newton,

Christopher R. Bohane, Thomas H. Connors, Brian E. Langenfeld and Susan A. Pereira, and each of them singly, as true and lawful attorneys, with full power to them and each of them to sign for each of the undersigned, in the names of, and in the capacities indicated below, any Registration Statement and any and all amendments thereto and to file the same with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission for the purpose of registering the Registrant as a management investment company under the Investment Company Act of 1940 and/or the shares issued by the Registrant under the Securities Act of 1933 granting unto my said attorneys, and each of them, acting alone, full power and authority to do and perform each and every act and thing requisite or necessary or desirable to be done in the premises, as fully to all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorneys or any of them may lawfully do or cause to be done by virtue thereof.

IN WITNESS WHEREOF, the undersigned have hereunto set their hand on this 7th day of December, 2012.

ROBERT E. BUTLER	Trustee
Robert E. Butler
MAUREEN R. GOLDFARB	Trustee
Maureen R. Goldfarb
DAVID H. GUNNING	Trustee
David H. Gunning
WILLIAM R. GUTOW	Trustee
William R. Gutow
MICHAEL HEGARTY	Trustee
Michael Hegarty
JOHN P. KAVANAUGH	Trustee
John P. Kavanaugh

ROBERT J. MANNING	Trustee
Robert J. Manning
J. DALE SHERRATT	Trustee
J. Dale Sherratt
LAURIE J. THOMSEN	Trustee
Laurie J. Thomsen
ROBERT W. UEK	Trustee
Robert W. Uek

MFS Series Trust I

MFS Series Trust II

MFS Series Trust III

MFS Series Trust IV

MFS Series Trust V

MFS Series Trust VI

MFS Series Trust VII

MFS Series Trust VIII

MFS Series Trust IX

MFS Series Trust X

MFS Series Trust XI

MFS Series Trust XII

MFS Series Trust XIII

MFS Series Trust XIV

MFS Series Trust XV

MFS Series Trust XVI

Massachusetts Investors Growth Stock Fund

Massachusetts Investors Trust

MFS Institutional Trust

MFS Municipal Series Trust

MFS Variable Insurance Trust

MFS Variable Insurance Trust II

MFS Variable Insurance Trust III

MFS California Municipal Fund

MFS Charter Income Trust

MFS Government Markets Income Trust

MFS High Income Municipal Trust

MFS High Yield Municipal Trust

MFS InterMarket Income Trust I

MFS Intermediate High Income Fund

MFS Intermediate Income Trust

MFS Investment Grade Municipal Trust

MFS Multimarket Income Trust

MFS Municipal Income Trust

MFS Special Value Trust

(each a “Registrant”)

POWER OF ATTORNEY

The undersigned, being the President and Principal Executive Officer, and Treasurer and Principal Financial and Accounting Officer, respectively, of each of the above-mentioned Registrants, hereby severally constitutes and appoints Mark N. Polebaum, Susan S. Newton, Christopher R. Bohane, Thomas H. Connors, Brian E.

Langenfeld and Susan A. Pereira, and each of them singly, as true and lawful attorneys, with full power to them and each of them to sign for each of the undersigned, in the names of, and in the capacities indicated below, any Registration Statement and any and all amendments thereto and to file the same with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission for the purpose of registering the Registrant as a management investment company under the Investment Company Act of 1940 and/or the shares issued by the Registrant under the Securities Act of 1933 granting unto my said attorneys, and each of them, acting alone, full power and authority to do and perform each and every act and thing requisite or necessary or desirable to be done in the premises, as fully to all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorneys or any of them may lawfully do or cause to be done by virtue thereof.

IN WITNESS WHEREOF, the undersigned have hereunto set their hand on this 7th day of December, 2012.

JOHN M. CORCORAN	President (Principal Executive Officer)
John M. Corcoran
DAVID L. DILORENZO	Principal Financial and Accounting Officer
David L. DiLorenzo

MFS SERIES TRUST XVI

MFS® GLOBAL MULTI-ASSET FUND

INDEX TO EXHIBITS

EXHIBIT NO.	DESCRIPTION OF EXHIBIT	PAGE NO.
101	Risk/Return summary of the fund’s prospectus as an Interactive Data File using eXtensible Business Reporting Language (“XBRL”)

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Prospectus Date	rr_ProspectusDate	Oct. 28, 2013

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

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MFS® Global Multi-Asset Fund Summary of Key Information

Objective [Heading]

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Investment Objective

Objective, Primary [Text Block]

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The fund’s investment objective is to seek total return.

Expense [Heading]

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Fees and Expenses

Expense Narrative [Text Block]

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This table describes the fees and expenses that you may pay when you buy and hold shares of the fund.

You may qualify for sales charge reductions if you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS Funds. More information about these and other waivers and reductions is available from your financial intermediary and in “Sales Charges and Waivers or Reductions” on page 12 of the fund’s prospectus and “Waivers of Sales Charges” on page H-1 of the fund’s Statement of Additional Information (“SAI”).

Shareholder Fees Caption [Text]

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Shareholder Fees (fees paid directly from your investment):

Operating Expenses Caption [Text]

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Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

Fee Waiver or Reimbursement over Assets, Date of Termination

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2014-10-31

Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These transaction costs, which are not reflected in “Annual Fund Operating Expenses” or in the “Example,” affect the fund’s performance.  During the most recent fiscal year, the fund’s portfolio turnover rate was 48% of the average value of its portfolio.

Portfolio Turnover, Rate

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48.00%

Expense Breakpoint Discounts [Text]

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You may qualify for sales charge reductions if you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS Funds.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

$ 50,000

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds.

The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods (unless otherwise indicated); your investment has a 5% return each year; and the fund’s operating expenses remain the same.

Expense Example by, Year, Caption [Text]

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Although your actual costs will likely be higher or lower, under these assumptions your costs would be:

Strategy [Heading]

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Principal Investment Strategies

Strategy Narrative [Text Block]

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MFS (Massachusetts Financial Services Company, the fund’s investment adviser) seeks to achieve the fund’s objective by generating returns from (1) a strategic allocation to a mix of asset classes, (2) individual security selection of U.S. and foreign issuers within those asset classes, and (3) a tactical asset allocation overlay to manage the fund’s exposure to asset classes, markets, and currencies primarily using derivative instruments. Derivatives include futures, forward contracts, options, structured securities, inverse floating rate instruments, and swaps.

The fund’s performance may not be correlated with the performance of the asset classes, markets, or currencies represented by the individual investments selected by MFS.

Strategic Asset Class Allocation:  MFS determines the percentages of the fund’s assets to be invested in the general asset classes of bonds and stocks, as well as in other less-traditional asset classes that MFS believes provide diversification benefits when added to a portfolio consisting of bonds and stocks, such as commodity-related investments and real estate-related investments.  As of October 1, 2013, the fund’s target strategic exposures among asset classes were as follows: 15% in inflation-adjusted debt instruments; 35% in other debt instruments; 30% in equity securities; 15% in commodity-related investments; and 5% in real estate-related investments.

Debt instruments include corporate bonds, U.S. Government securities, asset-backed securities, municipal instruments, foreign government securities, inflation-adjusted bonds, and other obligations to repay money borrowed.  Equity securities include common stocks, preferred stocks, securities convertible into stocks, equity interests in real estate investment trusts (REITs), and depositary receipts for such securities.

MFS may invest the fund’s assets in other mutual funds advised by MFS that invest in such asset classes instead of investing directly in such assets.

The strategic asset class allocations are not designed to take advantage of short-term market opportunities and have been selected for investment over longer time periods.  The strategic asset class allocations may be changed without shareholder approval or notice.  The actual strategic asset class weightings can deviate due to market movements and cash flows.  MFS periodically rebalances the fund’s strategic asset class weightings.  These target asset class weightings do not reflect the fund’s cash balance; some portion of the fund’s portfolio will be held in cash due to collateral requirements associated with the fund’s derivative transactions, purchase and redemption activity, and other short term cash needs.

Individual Security Selection:

In selecting direct investments for the fund, MFS may invest the fund’s assets in U.S. and foreign securities, including emerging market securities.

Of the fund’s investments in debt instruments, MFS primarily invests the fund’s assets in investment grade debt instruments, but may also invest in less than investment grade quality debt instruments (lower quality debt instruments).

MFS generally seeks to diversify the fund’s equity investments in terms of market capitalization (e.g., small, mid, large cap), style (e.g., growth, value), and location (e.g., U.S., foreign).  These allocations may vary significantly from time to time.

MFS may invest a large percentage of the fund’s assets in issuers in a single country, a small number of countries, or a particular geographic region.

While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives as part of its individual security selection process, MFS expects to use derivatives primarily to increase or decrease exposure to a particular market, segment of the market, or security, to increase or decrease interest rate or currency exposure, or as alternatives to direct investments.

A team of investment professionals selects investments for the fund. MFS allocates the fund’s assets to investment professionals by investment strategy. MFS uses a bottom-up investment approach to buying and selling investments for the fund. Investments are selected primarily based on fundamental analysis of individual issuers and instruments. Quantitative models that systematically evaluate issuers and instruments may also be considered.

Tactical Asset Allocation Overlay:  MFS employs a top-down tactical asset allocation process to adjust the fund’s exposure to asset classes, markets and currencies based on its assessment of the relative attractiveness of such asset classes, markets and currencies.  MFS manages the fund’s exposure to asset classes, markets and currencies primarily through the use of derivative instruments.

In managing the tactical overlay, MFS uses proprietary quantitative models and may increase or decrease the fund’s exposure to asset classes, markets and/or currencies resulting from MFS’ individual security selection based on MFS’ assessment of the risk/return potential of such asset classes, markets and/or currencies. After taking into account the tactical overlay, the fund’s exposure to the various asset classes, markets, and/or currencies may vary significantly from time to time. MFS may also expose the fund to asset classes, markets and/or currencies in which its individual security selection has resulted in no or little exposure (e.g., the high yield bond market).

MFS may adjust the fund’s net exposure to asset classes, markets and/or currencies by taking net short positions in an asset class, market or currency if MFS believes the risk/return potential of such asset class, market or currency is unattractive.  Alternatively, MFS may cause the fund to take net long positions in an asset class, market or currency if MFS believes such asset class, market or currency appears attractive.  After taking into account the tactical overlay, the fund’s net exposures to the asset classes referenced below, which may include exposure to U.S. and foreign issuers, will normally fall within the following ranges:

Asset Class	Range
Inflation-adjusted debt instruments	-5% to 35%
Debt instruments, excluding inflation-adjusted debt instruments	0% to 70%
Equity securities	0% to 60%
Commodity-related investments	-5% to 35%
Real estate-related investments	-10% to 20%

MFS’ tactical asset allocation process for the fund will typically make extensive use of derivatives.

MFS may also use derivatives to seek to limit the fund’s exposure to certain extreme market events.

Risk [Heading]

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Principal Risks

Risk Narrative [Text Block]

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As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.

The principal risks of investing in the fund are:

Investment Selection and Allocation Risk:  MFS’ investment analysis, its development and use of quantitative models,  its selection of investments, its assessment of the risk/return potential of asset classes, markets and currencies, and its adjustments to the fund’s exposure to asset classes, markets, and currencies may not produce the intended results and/or can lead to an investment focus that results in the fund underperforming other funds with similar investment strategies and/or underperforming the markets in which the fund invests.

Investment Strategy Risk:  The fund’s strategy to manage its exposure to asset classes, markets, and currencies may not produce the intended results. In addition, the strategies MFS may implement to limit the fund’s exposure to certain extreme market events may not work as intended, and the costs associated with such strategies will reduce the fund’s returns.

Interest Rate Risk:  The price of a debt instrument falls when interest rates rise and rises when interest rates fall. Instruments with longer maturities, or that do not pay current interest, are more sensitive to interest rate changes.

Credit Risk:  The price of a debt instrument depends, in part, on the credit quality of the issuer, borrower, counterparty, or other entity responsible for payment, or underlying collateral or assets and the terms of the instrument. The price of a debt instrument can decline in response to changes in the financial condition of the issuer, borrower, counterparty, or other entity, or underlying collateral or assets, or changes in specific or general market, economic, industry, political, regulatory, geopolitical, and other conditions.

Lower quality debt instruments (commonly referred to as “high yield securities” or “junk bonds”) can involve a substantially greater risk of default or can already be in default, and their values can decline significantly. Lower quality debt instruments are regarded as having predominantly speculative characteristics. Lower quality debt instruments tend to be more sensitive to adverse news about the issuer, or the market or economy in general, than higher quality debt instruments.

Stock Market/Company Risk:  Stock markets are volatile and can decline significantly in response to issuer, market, economic, industry, political, regulatory, geopolitical, and other conditions, as well as to investor perceptions of these conditions. The price of an equity security can decrease significantly in response to these conditions, and these conditions can affect a single issuer or type of security, issuers within a broad market sector, industry or geographic region, or the market in general.

Derivatives Risk:  Derivatives can be highly volatile and involve risks in addition to the risks of the underlying indicator(s) on which the derivative is based. Gains or losses from derivatives can be substantially greater than the derivatives’ original cost.  Derivatives can involve leverage.

Commodity Risk:  The value of commodities may be more volatile than the value of equity securities or debt instruments and their value may be affected by changes in overall market movements, commodity index volatility, changes in interest rates, or factors affecting a particular industry or commodity. The price of a commodity may be affected by demand/supply imbalances in the market for the commodity.

Real Estate-Related Investment Risk: The risks of investing in real estate-related securities include certain risks associated with the direct ownership of real estate and the real estate industry in general. These include risks related to general, regional and local economic conditions; fluctuations in interest rates and property tax rates; shifts in zoning laws, environmental regulations and other governmental action; cash flow dependency; increased operating expenses; lack of availability of mortgage funds; losses due to natural disasters; overbuilding; losses due to casualty or condemnation; changes in property values and rental rates; and other factors.  The securities of smaller real estate-related issuers can be more volatile and less liquid than securities of larger issuers and their issuers can have more limited financial resources.

Foreign and Emerging Markets Risk:  Exposure to foreign markets, especially emerging markets, through issuers or currencies can involve additional risks relating to market, economic, industry, political, regulatory, geopolitical, and other conditions. These factors can make foreign investments, especially those in emerging markets, more volatile and less liquid than U.S. investments. In addition, foreign markets can react differently to these conditions than the U.S. market. Emerging markets can have less developed markets, greater custody and operational risk, less developed legal, regulatory, and accounting systems, and greater political, social, and economic instability than developed markets.

Currency Risk:  The value of foreign currencies relative to the U.S. dollar fluctuates in response to market, economic, industry, political, regulatory, geopolitical, and other conditions, and a decline in the value of a foreign currency versus the U.S. dollar reduces the value in U.S. dollars of investments denominated in that foreign currency.

Geographic Concentration Risk: The fund’s performance could be closely tied to the market, currency, economic, political, regulatory, geopolitical, and other conditions in the countries or regions in which the fund invests and could be more volatile than the performance of more geographically-diversified funds.

Prepayment/Extension Risk:  Instruments subject to prepayment and/or extension can reduce the potential for gain for the instrument’s holders if the instrument is prepaid and increase the potential for loss if the maturity of the instrument is extended.

Inflation-Adjusted Debt Instruments Risk:  Interest payments on inflation-adjusted debt instruments can be unpredictable and vary based on the level of inflation. If inflation is negative, principal and income can both decline.

Municipal Risk:  The price of a municipal instrument can be volatile and significantly affected by adverse tax or court rulings, legislative or political changes, changes in specific or general market and economic conditions, and the financial condition of municipal issuers and insurers. Because many municipal instruments are issued to finance similar projects, conditions in these industries can significantly affect the fund and the overall municipal market.

Tax Risk:  In order to qualify as a regulated investment company (RIC) under the Internal Revenue Code of 1986, as amended, the fund must meet certain requirements regarding the source of its income, the diversification of its assets, and the distribution of its income. If the fund were to fail to qualify as a RIC and became subject to federal income tax, shareholders of the fund would be subject to the risk of diminished returns.

Leveraging Risk:  Leverage involves investment exposure in an amount exceeding the initial investment. Leverage can cause increased volatility by magnifying gains or losses.

Counterparty and Third Party Risk:  Transactions involving a counterparty or third party other than the issuer of the instrument are subject to the credit risk of the counterparty or third party, and to the counterparty’s or third party’s ability to perform in accordance with the terms of the transaction.

Liquidity Risk:  It may not be possible to sell certain investments, types of investments, and/or segments of the market at any particular time or at an acceptable price.

Risk Lose Money [Text]

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As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund.

Risk Not Insured Depository Institution [Text]

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An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.

Bar Chart and Performance Table [Heading]

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Performance Information

Performance Narrative [Text Block]

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The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing how the fund’s performance over time compares with that of a broad measure of market performance and one or more other measures of performance for markets in which the fund may invest.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.

Performance Information Illustrates Variability of Returns [Text]

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The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing how the fund's performance over time compares with that of a broad measure of market performance and one or more other measures of performance for markets in which the fund may invest.

Performance Additional Market Index [Text]

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As of December 31, 2012, the MFS Global Multi-Asset Blended Index (the "Blended Index") consisted of the following indices and weightings: 35% The Barclays Global Aggregate Bond Index; 15% Barclays U.S. Treasury Inflation Protected Securities (TIPS) Index; 15% The Dow Jones-UBS Commodity Index; 5% FTSE EPRA/NAREIT Developed Real Estate Index; and 30% MSCI All Country World Index. The components and weightings of the Blended Index may have differed during the period, and may differ in the future.

Performance Availability Phone [Text]

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1-800-225-2606

Performance Availability Website Address [Text]

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mfs.com

Performance Past Does Not Indicate Future [Text]

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The fund's past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.

Bar Chart [Heading]

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Class A Bar Chart.

Bar Chart Narrative [Text Block]

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The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund's shares. If these sales charges were included, they would reduce the returns shown.

Bar Chart Does Not Reflect Sales Loads [Text]

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The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund's shares. If these sales charges were included, they would reduce the returns shown.

Bar Chart Closing [Text Block]

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The total return for the nine-month period ended September 30, 2013 was (0.20)%. During the period(s) shown in the bar chart, the highest quarterly return was 5.55% (for the calendar quarter ended September 30, 2012) and the lowest quarterly return was (4.66)% (for the calendar quarter ended June 30, 2012).

Year to Date Return, Label

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total return

Bar Chart, Year to Date Return, Date

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Sep. 30, 2013

Bar Chart, Year to Date Return

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(0.20%)

Highest Quarterly Return, Label

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highest quarterly return

Highest Quarterly Return, Date

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Sep. 30, 2012

Highest Quarterly Return

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5.55%

Lowest Quarterly Return, Label

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lowest quarterly return

Lowest Quarterly Return, Date

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Jun. 30, 2012

Lowest Quarterly Return

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(4.66%)

Performance Table Heading

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Performance Table.

Index No Deduction for Fees, Expenses, Taxes [Text]

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(Reflects no deduction for fees, expenses or taxes)

Performance Table Uses Highest Federal Rate

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After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

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Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Performance Table One Class of after Tax Shown [Text]

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The after-tax returns are shown for only one of the fund's classes of shares, and after-tax returns for the fund's other classes of shares will vary from the returns shown.

Performance Table Closing [Text Block]

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After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.

Caption

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Average Annual Total Returns (for the Periods Ended December 31, 2012)

MSCI All Country World Index (gross div)

Risk/Return:

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Label

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Index Comparison (Reflects no deduction for fees, expenses or taxes) MSCI All Country World Index (gross div)

Average Annual Returns, 1 Year

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16.80%

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

2.91%

Average Annual Returns, Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 30, 2011

MFS Global Multi-Asset Blended Index

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Index Comparison (Reflects no deduction for fees, expenses or taxes) MFS Global Multi-Asset Blended Index

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

8.88%

^[1]

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

3.52%

^[1]

Average Annual Returns, Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 30, 2011

^[1]

A

Risk/Return:

rr_RiskReturnAbstract

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[2]

Management Fee

rr_ManagementFeesOverAssets

0.72%

Distribution and/or Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

1.09%

Acquired (Underlying) Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.17%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.23%

Fee Reductions and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.79%)

^[3]

Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements

rr_NetExpensesOverAssets

1.44%

Expenses Deferred Charges [Text Block]

rr_ExpensesDeferredChargesTextBlock

On shares purchased without an initial sales charge and redeemed within 18 months of purchase for shares purchased on or after August 1, 2012, and within 24 months of purchase for shares purchased prior to August 1, 2012.

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

713

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

1,161

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,633

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,934

Annual Return 2012

rr_AnnualReturn2012

8.76%

Label

rr_AverageAnnualReturnLabel

A Shares Returns Before Taxes

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

2.51%

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

(3.01%)

Average Annual Returns, Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 30, 2011

A | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

A Shares Returns After Taxes on Distributions

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

2.51%

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

(3.32%)

A | After Taxes on Distributions and Sale of Fund Shares

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

A Shares Returns After Taxes on Distributions and Sale of Fund Shares

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

1.63%

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

(2.69%)

B

Risk/Return:

rr_RiskReturnAbstract

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)

rr_MaximumDeferredSalesChargeOverOther

4.00%

Management Fee

rr_ManagementFeesOverAssets

0.72%

Distribution and/or Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

1.09%

Acquired (Underlying) Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.17%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.98%

Fee Reductions and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.79%)

^[3]

Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements

rr_NetExpensesOverAssets

2.19%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

622

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

1,147

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,698

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

3,066

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

222

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

847

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,498

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

3,066

Label

rr_AverageAnnualReturnLabel

B Shares Returns Before Taxes

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

4.03%

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

(2.65%)

Average Annual Returns, Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 30, 2011

C

Risk/Return:

rr_RiskReturnAbstract

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Management Fee

rr_ManagementFeesOverAssets

0.72%

Distribution and/or Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

1.09%

Acquired (Underlying) Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.17%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.98%

Fee Reductions and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.79%)

^[3]

Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements

rr_NetExpensesOverAssets

2.19%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

322

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

847

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,498

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

3,243

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

222

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

847

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,498

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

3,243

Label

rr_AverageAnnualReturnLabel

C Shares Returns Before Taxes

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

6.94%

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

(0.45%)

Average Annual Returns, Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 30, 2011

I

Risk/Return:

rr_RiskReturnAbstract

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)

rr_MaximumDeferredSalesChargeOverOther

none

Management Fee

rr_ManagementFeesOverAssets

0.72%

Distribution and/or Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

1.09%

Acquired (Underlying) Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.17%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.98%

Fee Reductions and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.79%)

^[3]

Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements

rr_NetExpensesOverAssets

1.19%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

121

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

545

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

994

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,243

Label

rr_AverageAnnualReturnLabel

I Shares Returns Before Taxes

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

9.03%

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

0.59%

Average Annual Returns, Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 30, 2011

R1

Risk/Return:

rr_RiskReturnAbstract

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)

rr_MaximumDeferredSalesChargeOverOther

none

Management Fee

rr_ManagementFeesOverAssets

0.72%

Distribution and/or Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

1.09%

Acquired (Underlying) Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.17%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.98%

Fee Reductions and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.79%)

^[3]

Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements

rr_NetExpensesOverAssets

2.19%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

222

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

847

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,498

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

3,243

Label

rr_AverageAnnualReturnLabel

R1 Shares Returns Before Taxes

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

7.88%

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

(0.44%)

Average Annual Returns, Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 30, 2011

R2

Risk/Return:

rr_RiskReturnAbstract

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)

rr_MaximumDeferredSalesChargeOverOther

none

Management Fee

rr_ManagementFeesOverAssets

0.72%

Distribution and/or Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.50%

Other Expenses

rr_OtherExpensesOverAssets

1.09%

Acquired (Underlying) Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.17%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.48%

Fee Reductions and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.79%)

^[3]

Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements

rr_NetExpensesOverAssets

1.69%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

172

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

697

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,249

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,756

Label

rr_AverageAnnualReturnLabel

R2 Shares Returns Before Taxes

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

8.45%

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

0.07%

Average Annual Returns, Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 30, 2011

R3

Risk/Return:

rr_RiskReturnAbstract

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)

rr_MaximumDeferredSalesChargeOverOther

none

Management Fee

rr_ManagementFeesOverAssets

0.72%

Distribution and/or Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

1.09%

Acquired (Underlying) Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.17%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.23%

Fee Reductions and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.79%)

^[3]

Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements

rr_NetExpensesOverAssets

1.44%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

147

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

621

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,123

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,503

Label

rr_AverageAnnualReturnLabel

R3 Shares Returns Before Taxes

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

8.74%

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

0.33%

Average Annual Returns, Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 30, 2011

R4

Risk/Return:

rr_RiskReturnAbstract

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)

rr_MaximumDeferredSalesChargeOverOther

none

Management Fee

rr_ManagementFeesOverAssets

0.72%

Distribution and/or Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

1.09%

Acquired (Underlying) Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.17%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.98%

Fee Reductions and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.79%)

^[3]

Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements

rr_NetExpensesOverAssets

1.19%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

121

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

545

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

994

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,243

Label

rr_AverageAnnualReturnLabel

R4 Shares Returns Before Taxes

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

8.92%

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

0.53%

Average Annual Returns, Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 30, 2011

R5

Risk/Return:

rr_RiskReturnAbstract

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)

rr_MaximumDeferredSalesChargeOverOther

none

Management Fee

rr_ManagementFeesOverAssets

0.72%

Distribution and/or Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

1.07%

Acquired (Underlying) Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.17%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.96%

Fee Reductions and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.78%)

^[3]

Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements

rr_NetExpensesOverAssets

1.18%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

120

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

540

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

985

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 2,222

Label

rr_AverageAnnualReturnLabel

R5 Shares Returns Before Taxes

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

9.03%

Average Annual Returns, Since Inception

rr_AverageAnnualReturnSinceInception

0.59%

Average Annual Returns, Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 30, 2011

[1] As of December 31, 2012, the MFS Global Multi-Asset Blended Index (the "Blended Index") consisted of the following indices and weightings: 35% The Barclays Global Aggregate Bond Index; 15% Barclays U.S. Treasury Inflation Protected Securities (TIPS) Index; 15% The Dow Jones-UBS Commodity Index; 5% FTSE EPRA/NAREIT Developed Real Estate Index; and 30% MSCI All Country World Index. The components and weightings of the Blended Index may have differed during the period, and may differ in the future.

[2] On shares purchased without an initial sales charge and redeemed within 18 months of purchase for shares purchased on or after August 1, 2012, and within 24 months of purchase for shares purchased prior to August 1, 2012.

[3] Massachusetts Financial Services Company has agreed in writing to bear the fund's expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs, and investment-related expenses (such as interest and borrowing expenses incurred in connection with the fund's investment activity, and fees and expenses associated with investments in investment companies and other similar investment vehicles), such that "Total Annual Fund Operating Expenses" do not exceed 1.27% of the fund's average daily net assets annually for each of Class A and Class R3 shares, 2.02% of the fund's average daily net assets annually for each of Class B, Class C, and Class R1 shares, 1.02% of the fund's average daily net assets annually for each of Class I and Class R4 shares, 1.52% of the fund's average daily net assets annually for Class R2 shares, and 1.01% of the fund's average daily net assets annually for Class R5 shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least October 31, 2014.

XML

MFS® Global Multi-Asset Fund

MFS® Global Multi-Asset Fund Summary of Key Information

Investment Objective

The fund’s investment objective is to seek total return.

Fees and Expenses

This table describes the fees and expenses that you may pay when you buy and hold shares of the fund.

You may qualify for sales charge reductions if you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS Funds. More information about these and other waivers and reductions is available from your financial intermediary and in “Sales Charges and Waivers or Reductions” on page 12 of the fund’s prospectus and “Waivers of Sales Charges” on page H-1 of the fund’s Statement of Additional Information (“SAI”).

Shareholder Fees (fees paid directly from your investment):

Shareholder Fees MFS® Global Multi-Asset Fund	A		B	C	I	R1	R2	R3	R4	R5
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	5.75%		none	none	none	none	none	none	none	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	1.00%	[1]	4.00%	1.00%	none	none	none	none	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

Annual Fund Operating Expenses MFS® Global Multi-Asset Fund		A	B	C	I	R1	R2	R3	R4	R5
Management Fee		0.72%	0.72%	0.72%	0.72%	0.72%	0.72%	0.72%	0.72%	0.72%
Distribution and/or Service (12b-1) Fees		0.25%	1.00%	1.00%	none	1.00%	0.50%	0.25%	none	none
Other Expenses		1.09%	1.09%	1.09%	1.09%	1.09%	1.09%	1.09%	1.09%	1.07%
Acquired (Underlying) Fund Fees and Expenses		0.17%	0.17%	0.17%	0.17%	0.17%	0.17%	0.17%	0.17%	0.17%
Total Annual Fund Operating Expenses		2.23%	2.98%	2.98%	1.98%	2.98%	2.48%	2.23%	1.98%	1.96%
Fee Reductions and/or Expense Reimbursements	[1]	(0.79%)	(0.79%)	(0.79%)	(0.79%)	(0.79%)	(0.79%)	(0.79%)	(0.79%)	(0.78%)
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements		1.44%	2.19%	2.19%	1.19%	2.19%	1.69%	1.44%	1.19%	1.18%

Example

This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds.

The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods (unless otherwise indicated); your investment has a 5% return each year; and the fund’s operating expenses remain the same.

Although your actual costs will likely be higher or lower, under these assumptions your costs would be:

Expense Example MFS® Global Multi-Asset Fund (USD $)	1 YEAR	3 YEARS	5 YEARS	10 YEARS
A	713	1,161	1,633	2,934
B	622	1,147	1,698	3,066
C	322	847	1,498	3,243
I	121	545	994	2,243
R1	222	847	1,498	3,243
R2	172	697	1,249	2,756
R3	147	621	1,123	2,503
R4	121	545	994	2,243
R5	120	540	985	2,222

Expense Example No Redemption MFS® Global Multi-Asset Fund (USD $)	1 YEAR	3 YEARS	5 YEARS	10 YEARS
B	222	847	1,498	3,066
C	222	847	1,498	3,243

Portfolio Turnover

The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These transaction costs, which are not reflected in “Annual Fund Operating Expenses” or in the “Example,” affect the fund’s performance.  During the most recent fiscal year, the fund’s portfolio turnover rate was 48% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund’s investment adviser) seeks to achieve the fund’s objective by generating returns from (1) a strategic allocation to a mix of asset classes, (2) individual security selection of U.S. and foreign issuers within those asset classes, and (3) a tactical asset allocation overlay to manage the fund’s exposure to asset classes, markets, and currencies primarily using derivative instruments. Derivatives include futures, forward contracts, options, structured securities, inverse floating rate instruments, and swaps.

The fund’s performance may not be correlated with the performance of the asset classes, markets, or currencies represented by the individual investments selected by MFS.

Strategic Asset Class Allocation:  MFS determines the percentages of the fund’s assets to be invested in the general asset classes of bonds and stocks, as well as in other less-traditional asset classes that MFS believes provide diversification benefits when added to a portfolio consisting of bonds and stocks, such as commodity-related investments and real estate-related investments.  As of October 1, 2013, the fund’s target strategic exposures among asset classes were as follows: 15% in inflation-adjusted debt instruments; 35% in other debt instruments; 30% in equity securities; 15% in commodity-related investments; and 5% in real estate-related investments.

Debt instruments include corporate bonds, U.S. Government securities, asset-backed securities, municipal instruments, foreign government securities, inflation-adjusted bonds, and other obligations to repay money borrowed.  Equity securities include common stocks, preferred stocks, securities convertible into stocks, equity interests in real estate investment trusts (REITs), and depositary receipts for such securities.

MFS may invest the fund’s assets in other mutual funds advised by MFS that invest in such asset classes instead of investing directly in such assets.

The strategic asset class allocations are not designed to take advantage of short-term market opportunities and have been selected for investment over longer time periods.  The strategic asset class allocations may be changed without shareholder approval or notice.  The actual strategic asset class weightings can deviate due to market movements and cash flows.  MFS periodically rebalances the fund’s strategic asset class weightings.  These target asset class weightings do not reflect the fund’s cash balance; some portion of the fund’s portfolio will be held in cash due to collateral requirements associated with the fund’s derivative transactions, purchase and redemption activity, and other short term cash needs.

Individual Security Selection:

In selecting direct investments for the fund, MFS may invest the fund’s assets in U.S. and foreign securities, including emerging market securities.

Of the fund’s investments in debt instruments, MFS primarily invests the fund’s assets in investment grade debt instruments, but may also invest in less than investment grade quality debt instruments (lower quality debt instruments).

MFS generally seeks to diversify the fund’s equity investments in terms of market capitalization (e.g., small, mid, large cap), style (e.g., growth, value), and location (e.g., U.S., foreign).  These allocations may vary significantly from time to time.

MFS may invest a large percentage of the fund’s assets in issuers in a single country, a small number of countries, or a particular geographic region.

While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives as part of its individual security selection process, MFS expects to use derivatives primarily to increase or decrease exposure to a particular market, segment of the market, or security, to increase or decrease interest rate or currency exposure, or as alternatives to direct investments.

A team of investment professionals selects investments for the fund. MFS allocates the fund’s assets to investment professionals by investment strategy. MFS uses a bottom-up investment approach to buying and selling investments for the fund. Investments are selected primarily based on fundamental analysis of individual issuers and instruments. Quantitative models that systematically evaluate issuers and instruments may also be considered.

Tactical Asset Allocation Overlay:  MFS employs a top-down tactical asset allocation process to adjust the fund’s exposure to asset classes, markets and currencies based on its assessment of the relative attractiveness of such asset classes, markets and currencies.  MFS manages the fund’s exposure to asset classes, markets and currencies primarily through the use of derivative instruments.

In managing the tactical overlay, MFS uses proprietary quantitative models and may increase or decrease the fund’s exposure to asset classes, markets and/or currencies resulting from MFS’ individual security selection based on MFS’ assessment of the risk/return potential of such asset classes, markets and/or currencies. After taking into account the tactical overlay, the fund’s exposure to the various asset classes, markets, and/or currencies may vary significantly from time to time. MFS may also expose the fund to asset classes, markets and/or currencies in which its individual security selection has resulted in no or little exposure (e.g., the high yield bond market).

MFS may adjust the fund’s net exposure to asset classes, markets and/or currencies by taking net short positions in an asset class, market or currency if MFS believes the risk/return potential of such asset class, market or currency is unattractive.  Alternatively, MFS may cause the fund to take net long positions in an asset class, market or currency if MFS believes such asset class, market or currency appears attractive.  After taking into account the tactical overlay, the fund’s net exposures to the asset classes referenced below, which may include exposure to U.S. and foreign issuers, will normally fall within the following ranges:

Asset Class	Range
Inflation-adjusted debt instruments	-5% to 35%
Debt instruments, excluding inflation-adjusted debt instruments	0% to 70%
Equity securities	0% to 60%
Commodity-related investments	-5% to 35%
Real estate-related investments	-10% to 20%

MFS’ tactical asset allocation process for the fund will typically make extensive use of derivatives.

MFS may also use derivatives to seek to limit the fund’s exposure to certain extreme market events.

Principal Risks

As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.

The principal risks of investing in the fund are:

Investment Selection and Allocation Risk:  MFS’ investment analysis, its development and use of quantitative models,  its selection of investments, its assessment of the risk/return potential of asset classes, markets and currencies, and its adjustments to the fund’s exposure to asset classes, markets, and currencies may not produce the intended results and/or can lead to an investment focus that results in the fund underperforming other funds with similar investment strategies and/or underperforming the markets in which the fund invests.

Investment Strategy Risk:  The fund’s strategy to manage its exposure to asset classes, markets, and currencies may not produce the intended results. In addition, the strategies MFS may implement to limit the fund’s exposure to certain extreme market events may not work as intended, and the costs associated with such strategies will reduce the fund’s returns.

Interest Rate Risk:  The price of a debt instrument falls when interest rates rise and rises when interest rates fall. Instruments with longer maturities, or that do not pay current interest, are more sensitive to interest rate changes.

Credit Risk:  The price of a debt instrument depends, in part, on the credit quality of the issuer, borrower, counterparty, or other entity responsible for payment, or underlying collateral or assets and the terms of the instrument. The price of a debt instrument can decline in response to changes in the financial condition of the issuer, borrower, counterparty, or other entity, or underlying collateral or assets, or changes in specific or general market, economic, industry, political, regulatory, geopolitical, and other conditions.

Lower quality debt instruments (commonly referred to as “high yield securities” or “junk bonds”) can involve a substantially greater risk of default or can already be in default, and their values can decline significantly. Lower quality debt instruments are regarded as having predominantly speculative characteristics. Lower quality debt instruments tend to be more sensitive to adverse news about the issuer, or the market or economy in general, than higher quality debt instruments.

Stock Market/Company Risk:  Stock markets are volatile and can decline significantly in response to issuer, market, economic, industry, political, regulatory, geopolitical, and other conditions, as well as to investor perceptions of these conditions. The price of an equity security can decrease significantly in response to these conditions, and these conditions can affect a single issuer or type of security, issuers within a broad market sector, industry or geographic region, or the market in general.

Derivatives Risk:  Derivatives can be highly volatile and involve risks in addition to the risks of the underlying indicator(s) on which the derivative is based. Gains or losses from derivatives can be substantially greater than the derivatives’ original cost.  Derivatives can involve leverage.

Commodity Risk:  The value of commodities may be more volatile than the value of equity securities or debt instruments and their value may be affected by changes in overall market movements, commodity index volatility, changes in interest rates, or factors affecting a particular industry or commodity. The price of a commodity may be affected by demand/supply imbalances in the market for the commodity.

Real Estate-Related Investment Risk: The risks of investing in real estate-related securities include certain risks associated with the direct ownership of real estate and the real estate industry in general. These include risks related to general, regional and local economic conditions; fluctuations in interest rates and property tax rates; shifts in zoning laws, environmental regulations and other governmental action; cash flow dependency; increased operating expenses; lack of availability of mortgage funds; losses due to natural disasters; overbuilding; losses due to casualty or condemnation; changes in property values and rental rates; and other factors.  The securities of smaller real estate-related issuers can be more volatile and less liquid than securities of larger issuers and their issuers can have more limited financial resources.

Foreign and Emerging Markets Risk:  Exposure to foreign markets, especially emerging markets, through issuers or currencies can involve additional risks relating to market, economic, industry, political, regulatory, geopolitical, and other conditions. These factors can make foreign investments, especially those in emerging markets, more volatile and less liquid than U.S. investments. In addition, foreign markets can react differently to these conditions than the U.S. market. Emerging markets can have less developed markets, greater custody and operational risk, less developed legal, regulatory, and accounting systems, and greater political, social, and economic instability than developed markets.

Currency Risk:  The value of foreign currencies relative to the U.S. dollar fluctuates in response to market, economic, industry, political, regulatory, geopolitical, and other conditions, and a decline in the value of a foreign currency versus the U.S. dollar reduces the value in U.S. dollars of investments denominated in that foreign currency.

Geographic Concentration Risk: The fund’s performance could be closely tied to the market, currency, economic, political, regulatory, geopolitical, and other conditions in the countries or regions in which the fund invests and could be more volatile than the performance of more geographically-diversified funds.

Prepayment/Extension Risk:  Instruments subject to prepayment and/or extension can reduce the potential for gain for the instrument’s holders if the instrument is prepaid and increase the potential for loss if the maturity of the instrument is extended.

Inflation-Adjusted Debt Instruments Risk:  Interest payments on inflation-adjusted debt instruments can be unpredictable and vary based on the level of inflation. If inflation is negative, principal and income can both decline.

Municipal Risk:  The price of a municipal instrument can be volatile and significantly affected by adverse tax or court rulings, legislative or political changes, changes in specific or general market and economic conditions, and the financial condition of municipal issuers and insurers. Because many municipal instruments are issued to finance similar projects, conditions in these industries can significantly affect the fund and the overall municipal market.

Tax Risk:  In order to qualify as a regulated investment company (RIC) under the Internal Revenue Code of 1986, as amended, the fund must meet certain requirements regarding the source of its income, the diversification of its assets, and the distribution of its income. If the fund were to fail to qualify as a RIC and became subject to federal income tax, shareholders of the fund would be subject to the risk of diminished returns.

Leveraging Risk:  Leverage involves investment exposure in an amount exceeding the initial investment. Leverage can cause increased volatility by magnifying gains or losses.

Counterparty and Third Party Risk:  Transactions involving a counterparty or third party other than the issuer of the instrument are subject to the credit risk of the counterparty or third party, and to the counterparty’s or third party’s ability to perform in accordance with the terms of the transaction.

Liquidity Risk:  It may not be possible to sell certain investments, types of investments, and/or segments of the market at any particular time or at an acceptable price.

Performance Information

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing how the fund’s performance over time compares with that of a broad measure of market performance and one or more other measures of performance for markets in which the fund may invest.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.

The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund's shares. If these sales charges were included, they would reduce the returns shown.

Class A Bar Chart.

The total return for the nine-month period ended September 30, 2013 was (0.20)%. During the period(s) shown in the bar chart, the highest quarterly return was 5.55% (for the calendar quarter ended September 30, 2012) and the lowest quarterly return was (4.66)% (for the calendar quarter ended June 30, 2012).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2012)

Average Annual Returns MFS® Global Multi-Asset Fund	Label	Average Annual Returns, 1 Year		Average Annual Returns, Since Inception		Average Annual Returns, Inception Date
B	B Shares Returns Before Taxes	4.03%		(2.65%)		Mar. 30, 2011
C	C Shares Returns Before Taxes	6.94%		(0.45%)		Mar. 30, 2011
I	I Shares Returns Before Taxes	9.03%		0.59%		Mar. 30, 2011
R1	R1 Shares Returns Before Taxes	7.88%		(0.44%)		Mar. 30, 2011
R2	R2 Shares Returns Before Taxes	8.45%		0.07%		Mar. 30, 2011
R3	R3 Shares Returns Before Taxes	8.74%		0.33%		Mar. 30, 2011
R4	R4 Shares Returns Before Taxes	8.92%		0.53%		Mar. 30, 2011
R5	R5 Shares Returns Before Taxes	9.03%		0.59%		Mar. 30, 2011
A	A Shares Returns Before Taxes	2.51%		(3.01%)		Mar. 30, 2011
After Taxes on Distributions A	A Shares Returns After Taxes on Distributions	2.51%		(3.32%)
After Taxes on Distributions and Sale of Fund Shares A	A Shares Returns After Taxes on Distributions and Sale of Fund Shares	1.63%		(2.69%)
MSCI All Country World Index (gross div)	Index Comparison (Reflects no deduction for fees, expenses or taxes) MSCI All Country World Index (gross div)	16.80%		2.91%		Mar. 30, 2011
MFS Global Multi-Asset Blended Index	Index Comparison (Reflects no deduction for fees, expenses or taxes) MFS Global Multi-Asset Blended Index	8.88%	[1]	3.52%	[1]	Mar. 30, 2011	[1]

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.

[1] On shares purchased without an initial sales charge and redeemed within 18 months of purchase for shares purchased on or after August 1, 2012, and within 24 months of purchase for shares purchased prior to August 1, 2012.

[1] Massachusetts Financial Services Company has agreed in writing to bear the fund's expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs, and investment-related expenses (such as interest and borrowing expenses incurred in connection with the fund's investment activity, and fees and expenses associated with investments in investment companies and other similar investment vehicles), such that "Total Annual Fund Operating Expenses" do not exceed 1.27% of the fund's average daily net assets annually for each of Class A and Class R3 shares, 2.02% of the fund's average daily net assets annually for each of Class B, Class C, and Class R1 shares, 1.02% of the fund's average daily net assets annually for each of Class I and Class R4 shares, 1.52% of the fund's average daily net assets annually for Class R2 shares, and 1.01% of the fund's average daily net assets annually for Class R5 shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least October 31, 2014.

[1] As of December 31, 2012, the MFS Global Multi-Asset Blended Index (the "Blended Index") consisted of the following indices and weightings: 35% The Barclays Global Aggregate Bond Index; 15% Barclays U.S. Treasury Inflation Protected Securities (TIPS) Index; 15% The Dow Jones-UBS Commodity Index; 5% FTSE EPRA/NAREIT Developed Real Estate Index; and 30% MSCI All Country World Index. The components and weightings of the Blended Index may have differed during the period, and may differ in the future.

XML

Document and Entity Information	0 Months Ended
	Jun. 30, 2013
Risk/Return:
Document Type	485BPOS
Document Period End Date	Jun. 30, 2013
Registrant Name	MFS SERIES TRUST XVI
Central Index Key	0000063067
Amendment Flag	false
Document Creation Date	Oct. 18, 2013
Document Effective Date	Oct. 28, 2013
Prospectus Date	Oct. 28, 2013
MFS® Global Multi-Asset Fund | A
Risk/Return:
Trading Symbol	GLMAX
MFS® Global Multi-Asset Fund | B
Risk/Return:
Trading Symbol	GLMBX
MFS® Global Multi-Asset Fund | C
Risk/Return:
Trading Symbol	GLMCX
MFS® Global Multi-Asset Fund | I
Risk/Return:
Trading Symbol	GLMIX
MFS® Global Multi-Asset Fund | R1
Risk/Return:
Trading Symbol	GLMRX
MFS® Global Multi-Asset Fund | R2
Risk/Return:
Trading Symbol	GLMSX
MFS® Global Multi-Asset Fund | R3
Risk/Return:
Trading Symbol	GLMTX
MFS® Global Multi-Asset Fund | R4
Risk/Return:
Trading Symbol	GLMUX
MFS® Global Multi-Asset Fund | R5
Risk/Return:
Trading Symbol	GLMVX