The main index ended 0.01 percent, or 0.56 points weaker at 5,744.99, its lowest level since March 20.
'Worries about high interest rates kept local buyers away from the market,' said a stockbroker on condition of anonymity.
Yields in T-bills rose for the fourth straight week at Monday's auction even though the central bank had kept its key policy rates unchanged for a third month in a row.,
Foreign investors were net buyers of 408.2 million rupees ($3.22 million) worth of shares, extending the year-to-date net foreign inflow to 4.95 billion rupees worth of shares.
Turnover was 938 million rupees, less than this year's daily average of 992 million rupees.
Stockbrokers said the market was concerned over a U.N. resolution passed last week that urged Sri Lanka to carry out credible investigations into killings and disappearances during its nearly 30-year civil war, in case non-compliance should lead to some form of sanctions.
The rupee fell to 126.85/90 to the dollar, easing from from Monday's close of 126.73/75, on light importer demand for dollars in dull trade, dealers said.
Both the stock and money markets were closed for a holiday on Tuesday. ($1 = 126.7500 Sri Lanka rupees)
(Reporting by Ranga Sirilal and Shihar Aneez; Editing by Simon Cameron-Moore)
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