The main share index fell 0.12 percent, or 6.94 points, to end at 5,730.54, its lowest since January 3.
The IMF said last week the economy faced high inflation and lower tax revenue risks, prompting speculation the government may turn to expensive commercial borrowing to bridge the budget gap, which would drive interest rate higher.
'Foreign selling and interest rates are worrying them,' said a stock broker.
The day's turnover was 763.5 million rupees ($6.02 million), less than this year's daily average of 1.11 billion rupees.
Foreign investors were net sellers of 223.97 million rupees worth of shares on Wednesday, extending the net foreign outflow so far this year to 838.56 million rupees.
The rupee ended weaker at 127.35/45 to the dollar, its lowest since January 3, from Tuesday's close of 127.20/30, dealers said.
Yields in T-bills were steady at a weekly auction on Wednesday at their near one-year low, after falling in the past 10 straight sessions.
($1 = 126.8000 Sri Lanka rupees)
(Reporting by Ranga Sirilal and Shihar Aneez; Editing by Sanjeev Miglani)
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