The main share index ended down 2.2 percent, or 134.05 points, at 5,951.83, its lowest close since April 24 and breaching the key support level of 6,000 points.
Analysts said investors were cautious over the fall in the rupee and earnings outlook. The local currency hit a near one-year low on Friday due to renewed selling of government bonds by foreign investors.
Shares in Ceylon Tobacco fell 12.64 percent to 1,108.20 rupees, while Nestle Lanka Plc dropped 5.21 percent to 2,205.20 rupees. Conglomerate John Keells Holdings fell 3.10 percent to 240.30 rupees.
Foreign investors were net sellers for a second straight session, selling 72.5 million rupees ($549,100) worth of shares.
But they have been net buyers of 18.35 billion rupees so far this year.
Turnover was 978 million rupees, more than this year's daily average of about 920.2 million rupees.
($1 = 132.0250 Sri Lanka rupees)
(Reporting by Ranga Sirilal and Shihar Aneez; Editing by Subhranshu Sahu)
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