A visiting IMF mission said Sri Lanka was facing additional risks from high inflation, lower tax revenue and slow structural reforms.
The main share index fell 0.16 percent, or 9.09 points, to end at 5,827.02, its lowest since Feb.7.
The central bank on Tuesday said authorities had decided not to pursue a new loan from the IMF, which had said it may not be in a position to consider any direct or indirect budget support to Sri Lanka.
"The concern is now if the interest rates will go up," a stockbroker said on condition of anonymity. "Since the expected IMF money is not going to materialise, Sri Lanka will need to go for expensive commercial borrowing."
Turnover was 608.44 million rupees ($4.82 million), less than this year's daily average of 1.17 billion rupees.
Foreign investors were net buyers of 159 million rupees worth of shares on Wednesday, but they have been net sellers of 1.1 billion rupees so far this year.
The rupee ended weaker at 126.40/60 to the dollar from Tuesday's close of 126.15/25, dealers said. ($1 = 126.3000 Sri Lanka rupees) (Reporting by Ranga Sirilal and Shihar Aneez; Editing by Ron Popeski)