The main stock index rose 0.31 percent, or 19.98 points, to close at 6,461.62.
'It was retail driven,' said a stockbroker on condition of anonymity.
Market turnover was 766.2 million rupees ($6.06 million) on Wednesday, less than this year's daily average of 1.05 billion rupees.
Foreign investors were net buyers of shares worth of 308.4 million rupees, extending net foreign inflows this year to 12.87 billion rupees.
The market 14-day Relative Strength Index (RSI) was in over-bought territory of 86.114 on Wednesday and has been above
the upper neutral level of 70 since April 16, Thomson Reuters data showed.
'Retailers are thinking that the market is not over heated yet and they will take the market to a different level. We see the resistance level at 6600 points,' the stockbroker said.
The bourse has gained 3.57 percent since the central bank cut key policy rates by 50 basis points on May 10, following some of its regional peers, to boost economic growth amid subdued demand.
A fall in interest rates of fixed income assets has helped boost sentiment in the share market as retail investors, who dominate the island nation's bourse in terms of volume, shift to equities from government securities.
The rupee ended steady at 126.25/30 in dull trade, currency dealers said.
($1 = 126.4000 Sri Lanka rupees)
(Reporting by Ranga Sirilal and Shihar Aneez; Editing by Anand Basu)
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