Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Prospectus Date	rr_ProspectusDate	Jul. 29, 2011
MFS New York Municipal Bond Fund (Prospectus Summary): \| MFS New York Municipal Bond Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return, Heading	rr_RiskReturnHeading	MFS ® New York Municipal Bond Fund
Supplement Text	ck0000751656_SupplementTextBlock	SUPPLEMENT TO PROSPECTUS The date of this supplement is September 28, 2011. MFS Ò Municipal Series Trust MFS ® New York Municipal Bond Fund Effective September 28, 2011, the sub-section entitled “Principal Investment Strategies” beneath the main heading "Summary of Key Information" is restated in its entirety as follows :
Investment Strategy, Heading	rr_StrategyHeading	Principal Investment Strategies
Investment Strategy, Narrative	rr_StrategyNarrativeTextBlock	The fund invests, under normal market conditions, at least 80% of its net assets in securities and other investments, the interest on which is exempt from federal income tax and personal income tax, if any, of New York. Interest from the fund’s investments may be subject to the federal alternative minimum tax. MFS (Massachusetts Financial Services Company, the fund's investment adviser) normally invests the fund’s assets primarily in municipal instruments. MFS may invest 25% or more of the fund’s assets in municipal instruments that finance similar projects, such as those relating to education, healthcare, housing, utilities, water or sewers. Municipal instruments whose interest is exempt from federal and state personal income tax include instruments issued by U.S. territories and possessions (such as Puerto Rico, Guam, and the U.S. Virgin Islands) and their political subdivisions and public corporations. Although MFS seeks to invest the fund’s assets in municipal instruments whose interest is exempt from federal and state personal income tax, MFS may also invest in taxable instruments. MFS primarily invests the fund’s assets in investment grade debt instruments, but may also invest in lower quality debt instruments. MFS invests a large percentage of the fund’s assets in municipal issuers of New York. While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives, 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 exposure, or as alternatives to direct investments. Derivatives include futures, forward contracts, options, structured securities, inverse floating rate instruments, and swaps. 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 instruments and their issuers in light of issuers’ current financial condition and current market, economic, political, and regulatory conditions. Factors considered may include the instrument’s credit quality, collateral characteristics, and indenture provisions, and the issuer’s management ability, capital structure, leverage, and ability to meet its current obligations. Quantitative models that systematically evaluate the structure of the debt instrument and its features may also be considered.
MFS New York Municipal Bond Fund \| A
Risk/Return:	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	MSNYX
MFS New York Municipal Bond Fund \| B
Risk/Return:	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	MBNYX
MFS New York Municipal Bond Fund \| C
Risk/Return:	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	MCNYX

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Prospectus Date

rr_ProspectusDate

Jul. 29, 2011

MFS New York Municipal Bond Fund (Prospectus Summary): | MFS New York Municipal Bond Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return, Heading

rr_RiskReturnHeading

MFS ® New York Municipal Bond Fund

Supplement Text

ck0000751656_SupplementTextBlock

SUPPLEMENT TO PROSPECTUS

The date of this supplement is September 28, 2011.

MFS Ò Municipal Series Trust

MFS ® New York Municipal Bond Fund

Effective September 28, 2011, the sub-section entitled “Principal Investment Strategies” beneath the main heading "Summary of Key Information" is restated in its entirety as follows :

Investment Strategy, Heading

rr_StrategyHeading

Principal Investment Strategies

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

The fund invests, under normal market conditions, at least 80% of its net assets in securities and other investments, the interest on which is exempt from federal income tax and personal income tax, if any, of New York. Interest from the fund’s investments may be subject to the federal alternative minimum tax.

MFS (Massachusetts Financial Services Company, the fund's investment adviser) normally invests the fund’s assets primarily in municipal instruments.

MFS may invest 25% or more of the fund’s assets in municipal instruments that finance similar projects, such as those relating to education, healthcare, housing, utilities, water or sewers. Municipal instruments whose interest is exempt from federal and state personal income tax include instruments issued by U.S. territories and possessions (such as Puerto Rico, Guam, and the U.S. Virgin Islands) and their political subdivisions and public corporations. Although MFS seeks to invest the fund’s assets in municipal instruments whose interest is exempt from federal and state personal income tax, MFS may also invest in taxable instruments.

MFS primarily invests the fund’s assets in investment grade debt instruments, but may also invest in lower quality debt instruments.

MFS invests a large percentage of the fund’s assets in municipal issuers of New York.

While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives, 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 exposure, or as alternatives to direct investments. Derivatives include futures, forward contracts, options, structured securities, inverse floating rate instruments, and swaps.

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 instruments and their issuers in light of issuers’ current financial condition and current market, economic, political, and regulatory conditions. Factors considered may include the instrument’s credit quality, collateral characteristics, and indenture provisions, and the issuer’s management ability, capital structure, leverage, and ability to meet its current obligations. Quantitative models that systematically evaluate the structure of the debt instrument and its features may also be considered.

MFS New York Municipal Bond Fund | A

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

MSNYX

MFS New York Municipal Bond Fund | B

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

MBNYX

MFS New York Municipal Bond Fund | C

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

MCNYX