The All Share Price Index closed at 2,858.54, down 0.59 percent (16.85 points) while the Milanka Price Index of more liquid stocks closed at 3,257.
48, down 0.48 percent (15.63 points).
Turnover was 293.7 million rupees, according to provisional Colombo Stock Exchange statistics.
"Trading activity was very low," said Charith Kamaladasa of Lanka Securities. "The very low investor particiapion was mainly owing to political uncertainty.
Also, historically December has been a dull month (for trading) because of the festive season."
The government has announced a snap presidential poll early next year.
The incumbent, President Mahinda Rajapaksa, is being challenged by Sarath Fonseka, a former defence forces chief, now named the common candidate of an opposition alliance.
Kamaladasa of Lanka Securities said stocks were also falling as investors booked profits on previous gains as they feared shares prices might fall further.
"In anticipation of the market falling further, investors are taking profits and looking to buy at lower prices in the future.
That selling pressure brought the index down."
Most shares, including blue chips, came down Wednesday.