The main index finished 0.53 percent, or 30.48 points weaker at 5,705.20, its lowest March 15.
'Interest rates are still high. They need to come off for retailers to get activated,' said a stockbroker on condition of anonymity.
Yields on T-bills rose for the fourth straight week at a March 25 auction even though the central bank had kept its key policy rates unchanged for a third month in a row.,
However, Central Bank Governor Ajith Nivard Cabraal on Monday told Reuters that market interest rates will ease this year as the monetary authority maintains a loose monetary policy stance.
Turnover was 403.2 million rupees ($3.18 million), less than half of this year's daily average of 1 billion rupees.
Foreign investors were net buyers of 6 million rupees worth of shares extending the year-to-date net foreign inflow to 4.98 billion rupees worth of shares.
The rupee gained to 126.30/35 to the dollar, from Thursday's close of 126.80/85, due to inflows from inward remittances, dealers said.
Both the stock and money markets were closed for a holiday on Friday.
($1 = 126.7500 Sri Lanka rupees)
(Reporting by Ranga Sirilal and Shihar Aneez; Editing by Kim Coghill)
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