The main index ended 0.27 percent higher at 5,704.53, its highest close since Feb. 22.
Analysts said many domestic investors stayed on the sidelines as yields on treasury bills rose for the second week on Wednesday even though the central bank kept its key policy rates unchanged for a third straight month.
Shares in the biggest listed lender, Commercial Bank of Ceylon, rose 1.79 percent to 114 rupees, while Hatton National Bank PLC rose 2.42 percent to 160.80 rupees.
Turnover was 309.34 million rupees ($2.45 million), well below this year's daily average of 1.02 billion rupees.
Foreign investors were net sellers of 5.9 million rupees worth of shares. They have been net buyers of 3.76 billion rupees worth of shares this year.
The rupee ended weaker at 126.30/35 to the dollar from Friday's close of 126.10/20, due to importer dollar demand, dealers said. ($1 = 126.1500 Sri Lanka rupees)
(Reporting by Ranga Sirilal and Shihar Aneez)
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