The main share index ended down 0.13 percent at 6,007.65, its lowest since July 9.
Conglomerate John Keells Holdings fell 0.6 percent to 247.10 rupees.
The index hit a near 10-week low on July 9 on concerns over the rupee's weakening trend and possible foreign outflows.
The local currency weakened to a near 10-month low early on
Tuesday due to importer demand for dollar and there was no central bank intervention.
Turnover on Tuesday was 737.8 million rupees ($5.63 million), provisional data showed, which was less than this year's daily average of about 970 million rupees.
($1 = 131.0250 Sri Lanka rupees)
(Reporting by Ranga Sirilal and Shihar Aneez; Editing by Gopakumar Warrier)