The main share index fell 0.68 percent to 5,635.90, its lowest since Dec. 28.
'Economic worries have hit sentiment after the IMF negative comments,' a stockbroker said on condition of anonymity. 'Retailers sold shares to settle outstanding credit transactions as it is the end of the month.'
The market has fallen 3.4 percent in thin volume since the IMF on Feb. 13 said Sri Lanka was facing slow growth, high inflation and lower tax revenue risks.
John Keells fell 0.76 percent to 234 rupees, while cigarette manufacturer Ceylon Tobacco Co. plummeted 5.95 percent to 721 rupees in thin volume.
Foreign buying accounted for around 75 percent of the day's turnover of 1.43 billion rupees ($11.22 million), more than this year's daily average of 1.06 billion rupees.
Foreign investors sold a net 20.7 million rupees worth of shares, extending the net foreign outflow so far this year to 215.55 million rupees.
The rupee edged down to 127.43/48 to the dollar on inflows from foreign remittances, dealers said. ($1 = 127.5 rupees)
(Reporting by Shihar Aneez; Editing by Nick Macfie)
(Reuters Messaging: email@example.com)