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

Eaton Vance Senior Income Trust as of June 30, 2006

MANAGEMENT’S DISCUSSION OF FUND PERFORMANCE

The Trust

Performance for the Year ended June 30, 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 8.46% for the year ended June 30, 2006. That return was the result of an increase in share price from $8.04 on June 30, 2005 to $8.13 on June 30, 2006 and the reinvestment of $0.569 in regular monthly dividends.(1)

•             Based on net asset value (NAV), the Trust had a total return of 7.02% for the year ended June 30, 2006. That return was the result of a decrease in NAV from $8.76 on June 30, 2005 to $8.74 on June 30, 2006, and the reinvestment of all distributions.(1)

•             Based on its June 2006 monthly dividend payment of $0.052 and a closing share price of $8.13, the Trust had a market yield of 7.68%.(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 6.06% for the year ended June 30, 2006.(3)

Management Discussion

•             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’s investments in senior floating-rate loans represented 401 borrowers at June 30, 2006. The Trust’s average loan size was 0.21% of total investments, and no industry constituted more than 7% of the Trust’s total investments. Health care, chemicals & plastics, building & development (which includes companies that manage/own apartments, shopping malls and commercial office buildings, among others), leisure goods/activities/movies, and business equipment & services were the Trust’s largest industry weightings.(4)

•             The loan market was characterized by higher interest rates, narrowing credit spreads and a soaring volume of new issues. The London Inter-Bank Offered Rate (LIBOR) – the benchmark over which loan interest rates are typically set – rose in lockstep with the Federal Reserve’s Federal Funds rate. Toward the end of the period, there were signs that spreads appeared to have bottomed, with lenders increasingly able to get more favorable terms on loans.

•             The Trust also had an 8.8% (of total investments) position in high-yield bonds, which was additive to total return on NAV. The high-yield bond segment remained focused on B-rated bonds and on shorter maturities, which provided more flexibility in times of increasing market volatility.

•             The Trust’s share price traded at a discount versus its NAV, as have many closed-end income funds that employ leverage. However, most of these funds buy fixed-rate investments and often use shorter and/or floating-rate instruments, which, in a rising interest rate environment, can impair a closed-end fund’s ability to earn and pay dividends. For this reason, closed-end income funds may trade flat-to-lower in a rising-rate climate, such as the one we have recently experienced. In contrast, the Trust invests primarily in floating rate instruments, which may add income in a rising interest rate environment. While it is difficult to attribute the Trust’s market share discount to NAV to one factor, we believe a likely cause was a market perception that rising rates impair the earning power of closed-end income funds. If this were the cause, management believes that the market failed to distinguish the floating-rate nature of most of the Trust’s assets. Although there is no certainty that the Trust will continue to do so, the Trust raised its dividend during the year ended June 30, 2006.

•             At June 30, 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.

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. 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.

Shares of the Trust 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. Yield will vary.

(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. (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 comprising 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. (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.

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Eaton Vance Senior Income Trust as of June 30, 2006

PERFORMANCE

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 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. 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 Fund’s current performance may be lower or higher than the quoted return.

The views expressed in 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 Eaton Vance disclaims any responsibility to update such views. These views may not be relied on as investment advice and, because investment decisions for an Eaton Vance fund are based on many factors, may not be relied on as an indication of trading intent on behalf of any Eaton Vance fund.

Diversification by Industries (2)

(2)   Reflects the Trust’s investments as of June 30, 2006. Industries are shown as a percentage of the Trust’s total investments. Portfolio information may not be representative of current or future investments and may change due to active management.

Trust Allocations (3)

By total invetsments

(3)        Trust Allocations are shown as a percentage of the Trust’s total investments as of June 30, 2006. Trust statistics may not be representative of current or future investments and are subject to change due to active management.

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