497

Eaton Vance Management

Two International Place

Boston, MA 02110

(617)482-8260

www.eatonvance.com

June 25, 2018

Securities and Exchange Commission

100 F Street, NE

Washington, DC 20549

Attn: Office of Filings, Information & Consumer Services

Re: Eaton Vance Special Investment Trust (the “Registrant”) (1933 Act File No. 002-27962) on behalf of Eaton Vance Large-Cap Value Fund (the “Fund”)

Ladies and Gentlemen:

On behalf of the Registrant and pursuant to Rule 497(e) under the Securities Act of 1933, as amended, attached for filing is an exhibit containing interactive data format risk/return summary information that mirrors the risk/return summary information in a Prospectus dated May 1, 2018 as revised June 18, 2018. The purpose of the filing is to submit the 497(e) filing dated June 18, 2018 in XBRL for the Fund.

Please contact me at (617) 672-8509 if you have any questions or comments.

Very truly yours,

/s/ Deanna R. Berry

Deanna R. Berry

Assistant Vice President

XML

Document and Entity Information	Total
Risk/Return:
Document Type	497
Document Period End Date	Dec. 31, 2017
Registrant Name	EATON VANCE SPECIAL INVESTMENT TRUST
Central Index Key	0000031266
Amendment Flag	false
Document Creation Date	Jun. 18, 2018
Document Effective Date	Jun. 18, 2018
Prospectus Date	May 01, 2018
Eaton Vance Large-Cap Value Fund | Class A
Risk/Return:
Trading Symbol	EHSTX
Eaton Vance Large-Cap Value Fund | Class C
Risk/Return:
Trading Symbol	ECSTX
Eaton Vance Large-Cap Value Fund | Class I
Risk/Return:
Trading Symbol	EILVX
Eaton Vance Large-Cap Value Fund | Class R
Risk/Return:
Trading Symbol	ERSTX
Eaton Vance Large-Cap Value Fund | Class R6
Risk/Return:
Trading Symbol	ERLVX

XML

Eaton Vance Large-Cap Value Fund

Investment Objective

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

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. Investors may also pay commissions or other fees to their financial intermediary when they buy and hold shares of the Fund, which are not reflected below. You may qualify for a reduced sales charge on purchases of Class A shares if you invest, or agree to invest over a 13-month period, at least $50,000 in Eaton Vance funds. Certain financial intermediaries also may offer variations in Fund sales charges to their customers as described in Appendix A – Financial Intermediary Sales Charge Variations in this Prospectus. More information about these and other discounts is available from your financial intermediary and in Sales Charges beginning on page 45 of this Prospectus and page 24 of the Fund’s Statement of Additional Information.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees - Eaton Vance Large-Cap Value Fund	Class A	Class C	Class I	Class R	Class R6
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	5.75%	none	none	none	none
Maximum Deferred Sales Charge (Load) (as a percentage of the lower of net asset value at purchase or redemption)	none	1.00%	none	none	none

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

Annual Fund Operating Expenses - Eaton Vance Large-Cap Value Fund	Class A	Class C	Class I	Class R	Class R6
Management Fees	0.62%	0.62%	0.62%	0.62%	0.62%
Distribution and Service (12b-1) Fees	0.25%	1.00%	none	0.50%	none
Other Expenses	0.19%	0.19%	0.19%	0.19%	0.11%
Total Annual Fund Operating Expenses	1.06%	1.81%	0.81%	1.31%	0.73%

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 then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, that the operating expenses remain the same and that any reimbursement arrangement remains in place for the contractual period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example - Eaton Vance Large-Cap Value Fund - USD ($)	1 Year	3 Years	5 Years	10 Years
Class A	677	893	1,126	1,795
Class C	284	569	980	2,127
Class I	83	259	450	1,002
Class R	133	415	718	1,579
Class R6	75	233	406	906

Expense Example, No Redemption - Eaton Vance Large-Cap Value Fund - USD ($)	1 Year	3 Years	5 Years	10 Years
Class A	677	893	1,126	1,795
Class C	184	569	980	2,127
Class I	83	259	450	1,002
Class R	133	415	718	1,579
Class R6	75	233	406	906

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” the portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These 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, Large-Cap Value Portfolio’s (the “Portfolio”), the Fund’s former master portfolio, portfolio turnover rate was 105% of the average value of its portfolio.

Principal Investment Strategies

Under normal market conditions, the Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in equity securities of large-cap companies (the “80% Policy”). The portfolio managers generally consider large-cap companies to be those companies having market capitalizations within the range of companies included in the Russell 1000^® Value Index, although the portfolio will generally consist of stocks with a market capitalization equal to or greater than the median market capitalization of companies included in such index.  As of December 31, 2017, the range of companies in the Russell 1000^® Value Index was $654 million to $489.1 billion and the median market capitalization was $9.7 billion. Under normal market conditions, the Fund invests primarily in value stocks. Value stocks are common stocks that, in the opinion of the investment adviser, are inexpensive or undervalued relative to the overall stock market. The Fund primarily invests in dividend-paying stocks, but also may invest in non-income producing stocks. The Fund may invest in convertible debt securities of any credit quality (including securities rated below investment grade (so-called “junk”)). The Fund may invest up to 25% of its total assets in foreign securities, some of which may be issued by companies domiciled in emerging market countries. As an alternative to holding foreign stocks directly, the Fund may invest in U.S. dollar-denominated securities of foreign companies that trade on U.S. exchanges or in the over-the-counter market (including depositary receipts that evidence ownership in underlying foreign stocks). The Fund may invest in exchange-traded funds (“ETFs”), a type of pooled investment vehicle, in order to manage cash positions or seek exposure to certain markets or market sectors. The Fund may also invest in publicly traded real estate investment trusts (“REITs”) and may lend its securities.

Investment decisions are made primarily on the basis of fundamental research. The portfolio managers utilize information provided by, and the expertise of, the investment adviser’s research staff in making investment decisions. In selecting stocks, the portfolio managers consider (among other factors) a company’s earnings or cash flow capabilities, dividend prospects, financial strength, growth potential, the strength of the company’s business franchises and management team, sustainability of a company’s competitiveness, and estimates of the company’s net value. The portfolio managers may sell a security when the investment adviser’s price objective for the security is reached, the fundamentals of the company deteriorate, a security’s price falls below acquisition cost or to pursue more attractive investment options. The portfolio managers seek to manage investment risk by maintaining broad issuer and industry diversification among the Fund’s holdings, and by conducting an analysis of the risk and return characteristics of securities (as described above) in which the Fund invests.

Principal Risks

Market Risk. The value of investments held by the Fund may increase or decrease in response to economic, political and financial events (whether real, expected or perceived) in the U.S. and global markets. The frequency and magnitude of such changes in value cannot be predicted. Certain securities and other investments held by the Fund may experience increased volatility, illiquidity, or other potentially adverse effects in reaction to changing market conditions. Actions taken by the U.S. Federal Reserve or foreign central banks to stimulate or stabilize economic growth, such as decreases or increases in short-term interest rates, could cause high volatility in markets.

Equity Securities Risk. The value of equity securities and related instruments may decline in response to adverse changes in the economy or the economic outlook; deterioration in investor sentiment; interest rate, currency, and commodity price fluctuations; adverse geopolitical, social or environmental developments; issuer and sector-specific considerations; or other factors. Market conditions may affect certain types of stocks to a greater extent than other types of stocks. If the stock market declines in value, the value of the Fund’s equity securities will also likely decline. Although prices can rebound, there is no assurance that values will return to previous levels.

Large-Cap Value Risk. Because the Fund normally invests primarily in value stocks of large-cap companies, it is subject to the risk of underperforming the overall stock market during periods in which stocks of such companies are out of favor and generate lower returns than the market as a whole.

Convertible Securities Risk. Convertible securities generally possess characteristics common to both equity and debt securities. In addition to risks associated with investing in income securities, such as interest rate and credit risks, convertible securities may be subject to issuer-specific and market risks generally applicable to equity securities. Convertible securities may also react to changes in the value of the common stock into which they convert, and are thus subject to equity investing and market risks. A convertible security may be converted at an inopportune time, which may decrease the Fund’s return.

Foreign Investment Risk. Foreign investments can be adversely affected by political, economic and market developments abroad, including the imposition of economic and other sanctions by the United States or another country. Foreign markets may be smaller, less liquid and more volatile than the major markets in the United States, and as a result, Fund share values may be more volatile. Trading in foreign markets typically involves higher expense than trading in the United States. The Fund may have difficulties enforcing its legal or contractual rights in a foreign country. Depositary receipts are subject to many of the risks associated with investing directly in foreign instruments.

Emerging Markets Investment Risk. Investment markets in emerging market countries are typically smaller, less liquid and more volatile than developed markets, and emerging market securities often involve greater risks than developed market securities.

Currency Risk. Exchange rates for currencies fluctuate daily. The value of foreign investments may be affected favorably or unfavorably by changes in currency exchange rates in relation to the U.S. dollar. Currency markets generally are not as regulated as securities markets and currency transactions are subject to settlement, custodial and other operational risks.

Lower Rated Investments Risk. Investments rated below investment grade and comparable unrated investments (sometimes referred to as “junk”) have speculative characteristics because of the credit risk associated with their issuers. Changes in economic conditions or other circumstances typically have a greater effect on the ability of issuers of lower rated investments to make principal and interest payments than they do on issuers of higher rated investments. An economic downturn generally leads to a higher non-payment rate, and a lower rated investment may lose significant value before a default occurs. Lower rated investments typically are subject to greater price volatility and illiquidity than higher rated investments.

ETF Risk. ETFs are subject to the risks of investing in the underlying securities or other investments. ETF shares may trade at a premium or discount to net asset value and are subject to secondary market trading risks. In addition, the Fund will bear a pro rata portion of the operating expenses of an ETF in which it invests. Other pooled investment vehicles generally are subject to risks similar to those of ETFs.

Real Estate Risk. Real estate investments are subject to risks associated with owning real estate, including declines in real estate values, increases in property taxes, fluctuations in interest rates, limited availability of mortgage financing, decreases in revenues from underlying real estate assets, declines in occupancy rates, changes in government regulations affecting zoning, land use, and rents, environmental liabilities, and risks related to the management skill and creditworthiness of the issuer. Companies in the real estate industry may also be subject to liabilities under environmental and hazardous waste laws, among others. REITs must satisfy specific requirements for favorable tax treatment and can involve unique risks in addition to the risks generally affecting the real estate industry. The Fund is not eligible for a deduction from dividends received from REITs that is available to individuals who invest directly in REITs. Changes in underlying real estate values may have an exaggerated effect to the extent that investments are concentrated in particular geographic regions or property types.

Securities Lending Risk. Securities lending involves a possible delay in recovery of the loaned securities or a possible loss of rights in the collateral if the borrower fails financially. The Fund could also lose money if the value of the collateral decreases.

Portfolio Turnover Risk. The annual portfolio turnover rate of the Fund may exceed 100%. A mutual fund with a high turnover rate (100% or more) may generate more capital gains and may involve greater expenses (which may reduce return) than a fund with a lower rate. Capital gains distributions will be made to shareholders if offsetting capital loss carry forwards do not exist.

Risks Associated with Active Management. The success of the Fund’s investment strategy depends on portfolio management’s successful application of analytical skills and investment judgment. Active management involves subjective decisions.

General Fund Investing Risks. The Fund is not a complete investment program and there is no guarantee that the Fund will achieve its investment objective. It is possible to lose money by investing in the Fund. The Fund is designed to be a long-term investment vehicle and is not suited for short-term trading. Investors in the Fund should have a long-term investment perspective and be able to tolerate potentially sharp declines in value. Purchase and redemption activities by Fund shareholders may impact the management of the Fund and its ability to achieve its investment objective(s). In addition, the redemption by one or more large shareholders or groups of shareholders of their holdings in the Fund could have an adverse impact on the remaining shareholders in the Fund. An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Performance

The following bar chart and table provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and how the Fund’s average annual returns over time compare with those of a broad-based securities market index. The returns in the bar chart are for Class A shares and do not reflect a sales charge. If the sales charge was reflected, the returns would be lower. Past performance (both before and after taxes) is not necessarily an indication of how the Fund will perform in the future. Updated Fund performance information can be obtained by visiting www.eatonvance.com.

For the ten years ended December 31, 2017, the highest quarterly total return for Class A was 15.09% for the quarter ended September 30, 2009, and the lowest quarterly return was -21.37% for the quarter ended December 31, 2008.

Average Annual Total Return as of December 31, 2017

Average Annual Total Returns - Eaton Vance Large-Cap Value Fund	One Year	Five Years	Ten Years	Inception Date
Class A	8.20%	10.97%	4.62%
Class A | After Taxes on Distributions	6.73%	8.17%	3.18%
Class A | After Taxes on Distributions and Sales	5.81%	8.26%	3.44%
Class C	12.96%	11.45%	4.45%
Class I	15.10%	12.56%	5.51%
Class R	14.50%	12.00%	4.97%
Class R6	15.25%	12.64%	5.54%	Jul. 01, 2014
Russell 1000® Value Index	13.66%	14.03%	7.10%

These returns reflect the maximum sales charge for Class A (5.75%) and any applicable contingent deferred sales charge (“CDSC”) for Class C. The Class R6 performance shown above for the period prior to July 1, 2014 (commencement of operations) is the performance of Class I shares at net asset value without adjustment for any differences in the expenses of the two classes. If adjusted for such differences, returns would be different. Investors cannot invest directly in an Index.

After-tax returns are calculated using the highest historical individual federal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on a shareholder’s tax situation and the actual characterization of distributions, and may differ from those shown. After-tax returns are not relevant to shareholders who hold shares in tax-deferred accounts or to shares held by non-taxable entities. After-tax returns for other Classes of shares will vary from the after-tax returns presented for Class A shares. Return After Taxes on Distributions for a period may be the same as Return Before Taxes for that period because no taxable distributions were made during that period. Also, Return After Taxes on Distributions and the Sale of Fund Shares for a period may be greater than or equal to Return After Taxes on Distributions for the same period because of losses realized on the sale of Fund shares.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Central Index Key

dei_EntityCentralIndexKey

0000031266

Eaton Vance Large-Cap Value Fund

Risk/Return:

rr_RiskReturnAbstract

Investment Objective, Heading

rr_ObjectiveHeading

Investment Objective

Investment Objective, Primary

rr_ObjectivePrimaryTextBlock

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

Expense, Heading

rr_ExpenseHeading

Fees and Expenses of the Fund

Expense, Narrative

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. Investors may also pay commissions or other fees to their financial intermediary when they buy and hold shares of the Fund, which are not reflected below. You may qualify for a reduced sales charge on purchases of Class A shares if you invest, or agree to invest over a 13-month period, at least $50,000 in Eaton Vance funds. Certain financial intermediaries also may offer variations in Fund sales charges to their customers as described in Appendix A – Financial Intermediary Sales Charge Variations in this Prospectus. More information about these and other discounts is available from your financial intermediary and in Sales Charges beginning on page 45 of this Prospectus and page 24 of the Fund’s Statement of Additional Information.

Shareholder Fees, Caption

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses, Caption

rr_OperatingExpensesCaption

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

Portfolio Turnover, Heading

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” the portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These 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, Large-Cap Value Portfolio’s (the “Portfolio”), the Fund’s former master portfolio, portfolio turnover rate was 105% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

105.00%

Expense Breakpoint, Discounts

rr_ExpenseBreakpointDiscounts

You may qualify for a reduced sales charge on purchases of Class A shares if you invest, or agree to invest over a 13-month period, at least $50,000 in Eaton Vance funds. Certain financial intermediaries also may offer variations in Fund sales charges to their customers as described in Appendix A – Financial Intermediary Sales Charge Variations in this Prospectus. More information about these and other discounts is available from your financial intermediary and in Sales Charges beginning on page 45 of this Prospectus and page 24 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required Amount

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

$ 50,000

Expense Example, Heading

rr_ExpenseExampleHeading

Example.

Expense Example, Narrative

rr_ExpenseExampleNarrativeTextBlock

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 then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, that the operating expenses remain the same and that any reimbursement arrangement remains in place for the contractual period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Investment Strategy, Heading

rr_StrategyHeading

Principal Investment Strategies

Investment Strategy, Narrative

rr_StrategyNarrativeTextBlock

Under normal market conditions, the Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in equity securities of large-cap companies (the “80% Policy”). The portfolio managers generally consider large-cap companies to be those companies having market capitalizations within the range of companies included in the Russell 1000^® Value Index, although the portfolio will generally consist of stocks with a market capitalization equal to or greater than the median market capitalization of companies included in such index.  As of December 31, 2017, the range of companies in the Russell 1000^® Value Index was $654 million to $489.1 billion and the median market capitalization was $9.7 billion. Under normal market conditions, the Fund invests primarily in value stocks. Value stocks are common stocks that, in the opinion of the investment adviser, are inexpensive or undervalued relative to the overall stock market. The Fund primarily invests in dividend-paying stocks, but also may invest in non-income producing stocks. The Fund may invest in convertible debt securities of any credit quality (including securities rated below investment grade (so-called “junk”)). The Fund may invest up to 25% of its total assets in foreign securities, some of which may be issued by companies domiciled in emerging market countries. As an alternative to holding foreign stocks directly, the Fund may invest in U.S. dollar-denominated securities of foreign companies that trade on U.S. exchanges or in the over-the-counter market (including depositary receipts that evidence ownership in underlying foreign stocks). The Fund may invest in exchange-traded funds (“ETFs”), a type of pooled investment vehicle, in order to manage cash positions or seek exposure to certain markets or market sectors. The Fund may also invest in publicly traded real estate investment trusts (“REITs”) and may lend its securities.

Investment decisions are made primarily on the basis of fundamental research. The portfolio managers utilize information provided by, and the expertise of, the investment adviser’s research staff in making investment decisions. In selecting stocks, the portfolio managers consider (among other factors) a company’s earnings or cash flow capabilities, dividend prospects, financial strength, growth potential, the strength of the company’s business franchises and management team, sustainability of a company’s competitiveness, and estimates of the company’s net value. The portfolio managers may sell a security when the investment adviser’s price objective for the security is reached, the fundamentals of the company deteriorate, a security’s price falls below acquisition cost or to pursue more attractive investment options. The portfolio managers seek to manage investment risk by maintaining broad issuer and industry diversification among the Fund’s holdings, and by conducting an analysis of the risk and return characteristics of securities (as described above) in which the Fund invests.

Strategy Portfolio Concentration

rr_StrategyPortfolioConcentration

Under normal market conditions, the Fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in equity securities of large-cap companies (the “80% Policy”). The portfolio managers generally consider large-cap companies to be those companies having market capitalizations within the range of companies included in the Russell 1000® Value Index, although the portfolio will generally consist of stocks with a market capitalization equal to or greater than the median market capitalization of companies included in such index. As of December 31, 2017, the range of companies in the Russell 1000® Value Index was $654 million to $489.1 billion and the median market capitalization was $9.7 billion. Under normal market conditions, the Fund invests primarily in value stocks. Value stocks are common stocks that, in the opinion of the investment adviser, are inexpensive or undervalued relative to the overall stock market. The Fund primarily invests in dividend-paying stocks, but also may invest in non-income producing stocks. The Fund may invest in convertible debt securities of any credit quality (including securities rated below investment grade (so-called “junk”)). The Fund may invest up to 25% of its total assets in foreign securities, some of which may be issued by companies domiciled in emerging market countries. As an alternative to holding foreign stocks directly, the Fund may invest in U.S. dollar-denominated securities of foreign companies that trade on U.S. exchanges or in the over-the-counter market (including depositary receipts that evidence ownership in underlying foreign stocks). The Fund may invest in exchange-traded funds (“ETFs”), a type of pooled investment vehicle, in order to manage cash positions or seek exposure to certain markets or market sectors. The Fund may also invest in publicly traded real estate investment trusts (“REITs”) and may lend its securities.

Risk, Heading

rr_RiskHeading

Principal Risks

Risk, Narrative

rr_RiskNarrativeTextBlock

Market Risk. The value of investments held by the Fund may increase or decrease in response to economic, political and financial events (whether real, expected or perceived) in the U.S. and global markets. The frequency and magnitude of such changes in value cannot be predicted. Certain securities and other investments held by the Fund may experience increased volatility, illiquidity, or other potentially adverse effects in reaction to changing market conditions. Actions taken by the U.S. Federal Reserve or foreign central banks to stimulate or stabilize economic growth, such as decreases or increases in short-term interest rates, could cause high volatility in markets.

Equity Securities Risk. The value of equity securities and related instruments may decline in response to adverse changes in the economy or the economic outlook; deterioration in investor sentiment; interest rate, currency, and commodity price fluctuations; adverse geopolitical, social or environmental developments; issuer and sector-specific considerations; or other factors. Market conditions may affect certain types of stocks to a greater extent than other types of stocks. If the stock market declines in value, the value of the Fund’s equity securities will also likely decline. Although prices can rebound, there is no assurance that values will return to previous levels.

Large-Cap Value Risk. Because the Fund normally invests primarily in value stocks of large-cap companies, it is subject to the risk of underperforming the overall stock market during periods in which stocks of such companies are out of favor and generate lower returns than the market as a whole.

Convertible Securities Risk. Convertible securities generally possess characteristics common to both equity and debt securities. In addition to risks associated with investing in income securities, such as interest rate and credit risks, convertible securities may be subject to issuer-specific and market risks generally applicable to equity securities. Convertible securities may also react to changes in the value of the common stock into which they convert, and are thus subject to equity investing and market risks. A convertible security may be converted at an inopportune time, which may decrease the Fund’s return.

Foreign Investment Risk. Foreign investments can be adversely affected by political, economic and market developments abroad, including the imposition of economic and other sanctions by the United States or another country. Foreign markets may be smaller, less liquid and more volatile than the major markets in the United States, and as a result, Fund share values may be more volatile. Trading in foreign markets typically involves higher expense than trading in the United States. The Fund may have difficulties enforcing its legal or contractual rights in a foreign country. Depositary receipts are subject to many of the risks associated with investing directly in foreign instruments.

Emerging Markets Investment Risk. Investment markets in emerging market countries are typically smaller, less liquid and more volatile than developed markets, and emerging market securities often involve greater risks than developed market securities.

Currency Risk. Exchange rates for currencies fluctuate daily. The value of foreign investments may be affected favorably or unfavorably by changes in currency exchange rates in relation to the U.S. dollar. Currency markets generally are not as regulated as securities markets and currency transactions are subject to settlement, custodial and other operational risks.

Lower Rated Investments Risk. Investments rated below investment grade and comparable unrated investments (sometimes referred to as “junk”) have speculative characteristics because of the credit risk associated with their issuers. Changes in economic conditions or other circumstances typically have a greater effect on the ability of issuers of lower rated investments to make principal and interest payments than they do on issuers of higher rated investments. An economic downturn generally leads to a higher non-payment rate, and a lower rated investment may lose significant value before a default occurs. Lower rated investments typically are subject to greater price volatility and illiquidity than higher rated investments.

ETF Risk. ETFs are subject to the risks of investing in the underlying securities or other investments. ETF shares may trade at a premium or discount to net asset value and are subject to secondary market trading risks. In addition, the Fund will bear a pro rata portion of the operating expenses of an ETF in which it invests. Other pooled investment vehicles generally are subject to risks similar to those of ETFs.

Real Estate Risk. Real estate investments are subject to risks associated with owning real estate, including declines in real estate values, increases in property taxes, fluctuations in interest rates, limited availability of mortgage financing, decreases in revenues from underlying real estate assets, declines in occupancy rates, changes in government regulations affecting zoning, land use, and rents, environmental liabilities, and risks related to the management skill and creditworthiness of the issuer. Companies in the real estate industry may also be subject to liabilities under environmental and hazardous waste laws, among others. REITs must satisfy specific requirements for favorable tax treatment and can involve unique risks in addition to the risks generally affecting the real estate industry. The Fund is not eligible for a deduction from dividends received from REITs that is available to individuals who invest directly in REITs. Changes in underlying real estate values may have an exaggerated effect to the extent that investments are concentrated in particular geographic regions or property types.

Securities Lending Risk. Securities lending involves a possible delay in recovery of the loaned securities or a possible loss of rights in the collateral if the borrower fails financially. The Fund could also lose money if the value of the collateral decreases.

Portfolio Turnover Risk. The annual portfolio turnover rate of the Fund may exceed 100%. A mutual fund with a high turnover rate (100% or more) may generate more capital gains and may involve greater expenses (which may reduce return) than a fund with a lower rate. Capital gains distributions will be made to shareholders if offsetting capital loss carry forwards do not exist.

Risks Associated with Active Management. The success of the Fund’s investment strategy depends on portfolio management’s successful application of analytical skills and investment judgment. Active management involves subjective decisions.

General Fund Investing Risks. The Fund is not a complete investment program and there is no guarantee that the Fund will achieve its investment objective. It is possible to lose money by investing in the Fund. The Fund is designed to be a long-term investment vehicle and is not suited for short-term trading. Investors in the Fund should have a long-term investment perspective and be able to tolerate potentially sharp declines in value. Purchase and redemption activities by Fund shareholders may impact the management of the Fund and its ability to achieve its investment objective(s). In addition, the redemption by one or more large shareholders or groups of shareholders of their holdings in the Fund could have an adverse impact on the remaining shareholders in the Fund. An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk, Lose Money

rr_RiskLoseMoney

The Fund is not a complete investment program and there is no guarantee that the Fund will achieve its investment objective. It is possible to lose money by investing in the Fund.

Risk, Not Insured Depository Institution

rr_RiskNotInsuredDepositoryInstitution

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

Bar Chart and Performance Table, Heading

rr_BarChartAndPerformanceTableHeading

Performance

Performance, Narrative

rr_PerformanceNarrativeTextBlock

The following bar chart and table provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and how the Fund’s average annual returns over time compare with those of a broad-based securities market index. The returns in the bar chart are for Class A shares and do not reflect a sales charge. If the sales charge was reflected, the returns would be lower. Past performance (both before and after taxes) is not necessarily an indication of how the Fund will perform in the future. Updated Fund performance information can be obtained by visiting www.eatonvance.com.

Performance, Information Illustrates Variability of Returns

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following bar chart and table provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and how the Fund’s average annual returns over time compare with those of a broad-based securities market index.

Performance Availability Website Address

rr_PerformanceAvailabilityWebSiteAddress

www.eatonvance.com

Performance Past Does Not Indicate Future

rr_PerformancePastDoesNotIndicateFuture

Past performance (both before and after taxes) is not necessarily an indication of how the Fund will perform in the future.

Bar Chart Does Not Reflect Sales Loads

rr_BarChartDoesNotReflectSalesLoads

The returns in the bar chart are for Class A shares and do not reflect a sales charge. If the sales charge was reflected, the returns would be lower.

Bar Chart, Closing

rr_BarChartClosingTextBlock

For the ten years ended December 31, 2017, the highest quarterly total return for Class A was 15.09% for the quarter ended September 30, 2009, and the lowest quarterly return was -21.37% for the quarter ended December 31, 2008.

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

For the ten years ended December 31, 2017, the highest quarterly total return for Class A was

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

15.09%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

and the lowest quarterly return was

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(21.37%)

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Return as of December 31, 2017

Performance Table Does Reflect Sales Loads

rr_PerformanceTableDoesReflectSalesLoads

These returns reflect the maximum sales charge for Class A (5.75%) and any applicable contingent deferred sales charge (“CDSC”) for Class C.

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the highest historical individual federal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on a shareholder’s tax situation and the actual characterization of distributions, and may differ from those shown.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

After-tax returns are not relevant to shareholders who hold shares in tax-deferred accounts or to shares held by non-taxable entities.

Performance Table One Class of after Tax Shown

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns for other Classes of shares will vary from the after-tax returns presented for Class A shares.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

Return After Taxes on Distributions for a period may be the same as Return Before Taxes for that period because no taxable distributions were made during that period. Also, Return After Taxes on Distributions and the Sale of Fund Shares for a period may be greater than or equal to Return After Taxes on Distributions for the same period because of losses realized on the sale of Fund shares.

Performance Table Footnotes, Reason Performance Information for Class Different from Immediately Preceding Period [Text]

rr_PerformanceTableFootnotesReasonPerformanceInformationForClassDifferentFromImmediatelyPrecedingPeriod

The Class R6 performance shown above for the period prior to July 1, 2014 (commencement of operations) is the performance of Class I shares at net asset value without adjustment for any differences in the expenses of the two classes. If adjusted for such differences, returns would be different.

Performance Table, Closing

rr_PerformanceTableClosingTextBlock

These returns reflect the maximum sales charge for Class A (5.75%) and any applicable contingent deferred sales charge (“CDSC”) for Class C. The Class R6 performance shown above for the period prior to July 1, 2014 (commencement of operations) is the performance of Class I shares at net asset value without adjustment for any differences in the expenses of the two classes. If adjusted for such differences, returns would be different. Investors cannot invest directly in an Index.

After-tax returns are calculated using the highest historical individual federal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on a shareholder’s tax situation and the actual characterization of distributions, and may differ from those shown. After-tax returns are not relevant to shareholders who hold shares in tax-deferred accounts or to shares held by non-taxable entities. After-tax returns for other Classes of shares will vary from the after-tax returns presented for Class A shares. Return After Taxes on Distributions for a period may be the same as Return Before Taxes for that period because no taxable distributions were made during that period. Also, Return After Taxes on Distributions and the Sale of Fund Shares for a period may be greater than or equal to Return After Taxes on Distributions for the same period because of losses realized on the sale of Fund shares.

Eaton Vance Large-Cap Value Fund | Russell 1000® Value Index

Risk/Return:

rr_RiskReturnAbstract

Index No Deduction for Fees, Expenses, Taxes

rr_IndexNoDeductionForFeesExpensesTaxes

(reflects no deductions for fees, expenses or taxes)

One Year

rr_AverageAnnualReturnYear01

13.66%

Five Years

rr_AverageAnnualReturnYear05

14.03%

Ten Years

rr_AverageAnnualReturnYear10

7.10%

Eaton Vance Large-Cap Value Fund | Class 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 the lower of net asset value at purchase or redemption)

rr_MaximumDeferredSalesChargeOverOfferingPrice

none

Management Fees

rr_ManagementFeesOverAssets

0.62%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.19%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.06%

1 Year

rr_ExpenseExampleYear01

$ 677

3 Years

rr_ExpenseExampleYear03

893

5 Years

rr_ExpenseExampleYear05

1,126

10 Years

rr_ExpenseExampleYear10

1,795

1 Year

rr_ExpenseExampleNoRedemptionYear01

677

3 Years

rr_ExpenseExampleNoRedemptionYear03

893

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,126

10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 1,795

Annual Return 2008

rr_AnnualReturn2008

(34.47%)

Annual Return 2009

rr_AnnualReturn2009

17.01%

Annual Return 2010

rr_AnnualReturn2010

10.05%

Annual Return 2011

rr_AnnualReturn2011

(4.48%)

Annual Return 2012

rr_AnnualReturn2012

15.77%

Annual Return 2013

rr_AnnualReturn2013

29.34%

Annual Return 2014

rr_AnnualReturn2014

10.96%

Annual Return 2015

rr_AnnualReturn2015

(1.08%)

Annual Return 2016

rr_AnnualReturn2016

9.56%

Annual Return 2017

rr_AnnualReturn2017

14.80%

One Year

rr_AverageAnnualReturnYear01

8.20%

Five Years

rr_AverageAnnualReturnYear05

10.97%

Ten Years

rr_AverageAnnualReturnYear10

4.62%

Eaton Vance Large-Cap Value Fund | Class A | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

One Year

rr_AverageAnnualReturnYear01

6.73%

Five Years

rr_AverageAnnualReturnYear05

8.17%

Ten Years

rr_AverageAnnualReturnYear10

3.18%

Eaton Vance Large-Cap Value Fund | Class A | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

One Year

rr_AverageAnnualReturnYear01

5.81%

Five Years

rr_AverageAnnualReturnYear05

8.26%

Ten Years

rr_AverageAnnualReturnYear10

3.44%

Eaton Vance Large-Cap Value Fund | Class 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 the lower of net asset value at purchase or redemption)

rr_MaximumDeferredSalesChargeOverOfferingPrice

1.00%

Management Fees

rr_ManagementFeesOverAssets

0.62%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.19%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.81%

1 Year

rr_ExpenseExampleYear01

$ 284

3 Years

rr_ExpenseExampleYear03

569

5 Years

rr_ExpenseExampleYear05

980

10 Years

rr_ExpenseExampleYear10

2,127

1 Year

rr_ExpenseExampleNoRedemptionYear01

184

3 Years

rr_ExpenseExampleNoRedemptionYear03

569

5 Years

rr_ExpenseExampleNoRedemptionYear05

980

10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 2,127

One Year

rr_AverageAnnualReturnYear01

12.96%

Five Years

rr_AverageAnnualReturnYear05

11.45%

Ten Years

rr_AverageAnnualReturnYear10

4.45%

Eaton Vance Large-Cap Value Fund | Class 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 the lower of net asset value at purchase or redemption)

rr_MaximumDeferredSalesChargeOverOfferingPrice

none

Management Fees

rr_ManagementFeesOverAssets

0.62%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.19%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.81%

1 Year

rr_ExpenseExampleYear01

$ 83

3 Years

rr_ExpenseExampleYear03

259

5 Years

rr_ExpenseExampleYear05

450

10 Years

rr_ExpenseExampleYear10

1,002

1 Year

rr_ExpenseExampleNoRedemptionYear01

83

3 Years

rr_ExpenseExampleNoRedemptionYear03

259

5 Years

rr_ExpenseExampleNoRedemptionYear05

450

10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 1,002

One Year

rr_AverageAnnualReturnYear01

15.10%

Five Years

rr_AverageAnnualReturnYear05

12.56%

Ten Years

rr_AverageAnnualReturnYear10

5.51%

Eaton Vance Large-Cap Value Fund | Class R

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 the lower of net asset value at purchase or redemption)

rr_MaximumDeferredSalesChargeOverOfferingPrice

none

Management Fees

rr_ManagementFeesOverAssets

0.62%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.50%

Other Expenses

rr_OtherExpensesOverAssets

0.19%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.31%

1 Year

rr_ExpenseExampleYear01

$ 133

3 Years

rr_ExpenseExampleYear03

415

5 Years

rr_ExpenseExampleYear05

718

10 Years

rr_ExpenseExampleYear10

1,579

1 Year

rr_ExpenseExampleNoRedemptionYear01

133

3 Years

rr_ExpenseExampleNoRedemptionYear03

415

5 Years

rr_ExpenseExampleNoRedemptionYear05

718

10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 1,579

One Year

rr_AverageAnnualReturnYear01

14.50%

Five Years

rr_AverageAnnualReturnYear05

12.00%

Ten Years

rr_AverageAnnualReturnYear10

4.97%

Eaton Vance Large-Cap Value Fund | Class R6

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 the lower of net asset value at purchase or redemption)

rr_MaximumDeferredSalesChargeOverOfferingPrice

none

Management Fees

rr_ManagementFeesOverAssets

0.62%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.11%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.73%

1 Year

rr_ExpenseExampleYear01

$ 75

3 Years

rr_ExpenseExampleYear03

233

5 Years

rr_ExpenseExampleYear05

406

10 Years

rr_ExpenseExampleYear10

906

1 Year

rr_ExpenseExampleNoRedemptionYear01

75

3 Years

rr_ExpenseExampleNoRedemptionYear03

233

5 Years

rr_ExpenseExampleNoRedemptionYear05

406

10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 906

One Year

rr_AverageAnnualReturnYear01

15.25%

Five Years

rr_AverageAnnualReturnYear05

12.64%

Ten Years

rr_AverageAnnualReturnYear10

5.54%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 01, 2014

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	497
Document Period End Date	dei_DocumentPeriodEndDate	Dec. 31, 2017
Registrant Name	dei_EntityRegistrantName	EATON VANCE SPECIAL INVESTMENT TRUST
Central Index Key	dei_EntityCentralIndexKey	0000031266
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Jun. 18, 2018
Document Effective Date	dei_DocumentEffectiveDate	Jun. 18, 2018
Prospectus Date	rr_ProspectusDate	May 01, 2018