The island nation's main share index fell 0.15 percent or 9.02 points to 5,851.94, lowest since Nov. 25.
The day's turnover was 382.1 million Sri Lanka rupees ($3.35 million), lowest since Dec. 14, 2009, and well below last year's
average of 2.4 billion and this year's 2.3 billion.
Total volume was 13.6 million shares, the lowest since Nov. 11, against a five-day average of 19.7 million. The 30-day and
90-day average trading volumes were 47.3 million and 93.1 million. Last year's daily average was 67.9 million.
Market heavyweight John Keells Holdings PLC, which fell 1.7 percent to 167.30 rupees, led the market fall.
The bourse saw a net foreign outflow of 39.4 million rupees on Tuesday, and foreign investors have sold 18.2 billion thus far in 2011, and a record 26.4 billion in 2010.
The Colombo Stock Exchange is Asia's 11th-best performer with a year-to-date loss of 11.8 percent after being at the top
until June. It delivered Asia's best returns in 2009 and 2010.
The rupee closed flat at 113.89/90 rupees a dollar for a 20th day despite dollar demand, as the central bank spent $10 million defending it, dealers said