The main stock index closed down 0.49 percent at 7,050.87, its lowest close since July 15.
Foreign investors were net sellers of 87.4 million rupees worth of shares on Wednesday extending the year-to-date net foreign outflow to 3.16 billion rupees.
"Budget is the holding factor as investors are looking for clear direction," said Reshan Kurukulasuriya, chief operating officer of Richard Pieris Securities (Pvt) Ltd.
The new government, which was elected after the Aug. 17 polls, will present its maiden budget in November.
Shares of conglomerate John Keells fell 1.74 percent while Nestle Lanka Plc fell 0.06 percent. Shares in biggest listed banker Commercial Bank of Ceylon fell 1.79 percent.
Turnover was 1.29 billion rupees ($9.14 million), slightly above this year's daily average of 1.12 billion.
(reuters.com)