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, 2005

MANAGEMENT’S DISCUSSION OF FUND PERFORMANCE

The Trust

Performance for the Period ended June 30, 2005

•      Based on its June 2005 monthly dividend payment of $0.041 and a closing share price of $8.04, Eaton Vance Senior Income Trust, a closed-end fund traded on the New York Stock Exchange (the “Trust”), had a market yield of 6.12%.(1)

•      Based on share price (traded on the New York Stock Exchange), the Trust had a total return of -10.42% for the year ended June 30, 2005.  That return was the result of a decrease in share price from $9.46 on June 30, 2004 to $8.04 on June 30, 2005 and the reinvestment of $0.456 in regular monthly dividends.(2)

•      Based on net asset value, the Trust had a total return of 5.16% for the year ended June 30, 2005. That return was the result of a decrease in net asset value per share from $8.78 on June 30, 2004 to $8.76 on June 30, 2005, and the reinvestment of all distributions.(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 4.33% for the year ended June 30, 2005.(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, secured loans.

•      The Trust’s investments in senior floating-rate loans represented 373 borrowers at June 30, 2005 and reflected a continued effort at diversification. The Trust’s average loan size was just 0.23% of loan assets, and no industry constituted more than 7% of the Trust’s total loan investments. Building and development (which includes companies that manage/own apartments, shopping malls and commercial office buildings, among others), health care, cable and satellite telvision, leisure goods/activities/movies and publishing were the Trust’s largest sector weightings.*

•      Credit conditions remained relatively strong during the period, as companies in the Trust generally produced sufficient cash flow to meet debt service requirements. No specific sectors significantly underperformed within the Trust’s portfolio. At this point in the credit cycle, we currently expect to maintain a relatively high quality portfolio, especially given the heightened liquidity and general loosening of credit standards.

•      Supply-and-demand factors for the loan asset class varied during the period, resulting in a small downward movement in the Trust’s NAV per share. Demand exceeded supply in the first quarter of 2005, but waned slightly in the second quarter, as certain crossover investors sold loans to take advantage of wider spreads in the high-yield bond market. At the end of the period, with the loan supply having steadied, technical factors appeared to be more balanced.

•      Due to tight credit spreads in the high-yield bond market in the fall of 2004, the Trust continued to limit its exposure. As a percentage of each of net assets and total investments, high-yield bonds represented 16.5 and 9.7%, respectively, at June 30, 2005. A relatively low weighting limited potential NAV volatility when high-yield spreads widened in the first quarter of 2005.

•      At June 30, 2005, the Trust had leverage in the amount of approximately 42% of the Trust’s total assets. The Trust employs leverage through the issuance of Auction Preferred Shares (APS) and participation in a commercial paper program. 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 in cost of the Trust’s leverage may be offset by increased income from the Trust’s senior loan investments.

*      Holdings and industry weightings are subject to change due to active management.

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)  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.

(2)  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.

(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)  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, 2005

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 total investments as of June 30, 2005. Industries are shown as a percentage of the Trust’s total investments. Statistics may not be representative of current or future investments and may change due to active management.

Diversification(3)

By investment type

(3)   Reflects the Trust’s investments as of June 30, 2005. Investment types are shown as a percentage of the Trust’s total investments. Statistics may not be representative of current or future investments and may change due to active management.

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