The main share index ended 0.5 percent, or 30.79 points, down at 6,085.88, its lowest close since July 31.
Stockbrokers said concerns over the rupee volatility and earning fears dented sentiment.
Analysts said investors were cautious over the fall in the rupee. The local currency hit a new 11-1/2-month low on Thursday due to importer dollar demand.
Shares in Nestle Lanka Plc fell 0.6 percent to 2,326.50 rupees, while conglomerate John Keells Holdings Plc fell 0.56 percent to 248 rupees.
Foreign investors were net sellers for the first time in six sessions, selling 92.5 million rupees ($701,300) worth of shares. But they have been net buyers of 18.42 billion rupees so far this year.
Turnover was 652.8 million rupees, below this year's daily average of about 919.8 million rupees.
($1 = 131.9000 Sri Lanka rupees)
(Reporting by Ranga Sirilal and Shihar Aneez; Editing by Anand Basu)
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