UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED
MANAGEMENT INVESTMENT COMPANIES

Item 1. Reports to Stockholders

Performance for the Six Months ended December 31, 2006

·                  Based on share price, Eaton Vance Senior Income Trust (the “Trust”), a closed-end fund traded on the New York Stock Exchange, had a total return of 6.32% for the six months ended December 31, 2006. That return was the result of an increase in share price to $8.31 on December 31, 2006, from $8.13 on June 30, 2006, and the reinvestment of $0.324 in all distributions since June 30, 2006.(1)

·                  Based on net asset value (NAV), the Trust had a total return of 4.13% for the six months ended December 31, 2006. That return was the result of an increase in NAV per share to $8.75 on December 31, 2006, from $8.74 on June 30, 2006, and the reinvestment of $0.324 in monthly distributions.(1)

·                  Based on its December 31, 2006 monthly dividend payment of $0.056 and a closing share price of $8.31, the Trust had a market yield of 8.09%.(2)

·                  For performance comparison, the S&P/LSTA Leveraged Loan Index – an unmanaged index of U.S. dollar-denominated leveraged loans – had a total return of 3.62% for the six months ended December 31, 2006.(3)

Investment Environment

·                  The Trust is a closed-end fund and trades on the New York Stock Exchange under the symbol “EVF.”The Trust’s investment objective is to provide a high level of current income, consistent with preservation of capital, by investing primarily in senior loans. The Trust also employs leverage through the issuance of preferred shares and participation in a commercial paper program.

·                  The loan market enjoyed relatively stable fundamentals during the six months ended December 31, 2006, with default rates remaining low by historical standards. Technical factors came more into balance, as record new issuance from strong merger and acquisition activity met robust investor demand. Loan credit spreads stabilized following a period during which they had narrowed.

·                  The Federal Reserve raised its Federal Funds rate – a key short-term interest rate benchmark – by 25 basis points (0.25%) at its June meeting, to 5.25%. The London Inter-Bank Offered Rate (LIBOR) – the benchmark over which loan interest rates are typically set – rose in step with that action, increasing the Trust’s total return.

The Trust’s Investments

·                  At December 31, 2006, the Trust’s investments included 459 borrowers respresenting 39 industries, with an average loan size of 0.19% of total investments, and no industry constituting more than 7.5% of total investments. Health care, chemicals and plastics, business equipment and services, leisure goods/activities/movies and building and development (including manufacturers of building products and companies that manage/own apartments, shopping malls and commercial office buildings, among others)were the Trust’s largest industry weightings.(4)

·                  At December 31, 2006, the Trust had leverage in the amount of approximately 42% of the Trust’s total assets. The Trust employs leverage though the issuance of Auction Preferred Shares (APS) and a commercial paper program.(5) Use of financial leverage creates an opportunity for increased income but, at the same time, creates special risks (including the likelihood of greater volatility of net asset value and market price of common shares). The cost of leverage rises and falls with changes in short-term interest rates. Such increases/decreases in the cost of the Trust’s leverage may be offset by increased/decreased income from the Trust’s senior loan investments.

(1)       Performance results reflect the effect of leverage resulting from the Trust’s issuance of Auction Preferred Shares and participation in a commercial paper program.(2) The Trust’s market yield is calculated by dividing the most recent dividend per share by the share market price at the end of the period and annualizing the result.(3) It is not possible to invest directly in an Index. The Index’s total return reflects changes in value of the loans constituting the Index and accrual of interest and does not reflect the commissions or expenses that would have been incurred if an investor individually purchased or sold the loans represented in the Index. Unlike the Trust, the Index’s return does not reflect the effect of leverage, such as the issuance of Auction Preferred Shares and participation in a commercial paper program.(4) Holdings and industry weightings are subject to change due to active management. (5) In the event of a rise in long-term interest rates, the value of the Trust’s investment portfolio could decline, which would reduce the asset coverage for its Auction Preferred Shares.

Past performance is no guarantee of future results. Returns are historical and are calculated by determining the percentage change in net asset value or share price (as applicable) with all distributions reinvested. The returns do not include dividends declared in December 2006 and payable in 2007. Investment return and principal value will fluctuate so that shares, when sold, may be worth more or less than their original cost. Performance is for the stated time period only; due to market volatility, the Trust’s current performance may be lower or higher than the quoted return.

Trust shares are not insured by the FDIC and are not deposits or other obligations of, or guaranteed by, any depository institution. Shares are subject to investment risks, including possible loss of principal invested.

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Performance(1)

(1)       Performance results reflect the effect of leverage resulting from the Trust’s issuance of Auction Preferred Shares and its participation in a commercial paper program. In the event of a rise in long-term interest rates, the value of the Trust’s investment portfolio could decline, which would reduce the asset coverage for itsAuction Preferred Shares.

Past performance is no guarantee of future results. Returns are historical and are calculated by determining the percentage change in net asset value or share price (as applicable) with all distributions reinvested. The returns do not include dividends declared in December 2006 and payable in 2007. Investment return and principal value will fluctuate so that shares, when redeemed, may be worth more or less than their original cost. Performance is for the stated time period only; due to market volatility, the Trust’s current performance may be lower or higher than the quoted return.

The views expressed throughout this report are those of the portfolio managers and are current only through the end of the period of the report as stated on the cover. These views are subject to change at any time based upon market or other conditions, and the investment adviser disclaims any responsibility to update such views. These views may not be relied on as investment advice and, because investment decisions for a fund are based on many factors, may not be relied on as an indication of trading intent on behalf of any Eaton Vance fund.

Trust Allocations(2)

By Total Investments

(2)          Trust Allocations are shown as a percentage of total investments as of December 31, 2006. Allocations may not be representative of the Trust’s current or future investments and are subject to change due to active management.

Diversification by Industries(3)

By Total Investments

(3)          Reflects the Trust’s investments as of December 31, 2006. Industries are shown as a percentage of the Trust’s total investments. Statistics may not be representative of current or future investments and are subject to change due to active management.

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