The Milanka index - which tracks the most liquid and highly capitalised stocks - rose a provisional 0.6 percent, or 12.47 points, to 2,081.49 points.
"Most broker houses were on half day and investors were on holiday," said one broker. President Chandrika Kumaratunga has proclaimed December 31 a day of national mourning.
Sri Lanka Telecom Ltd rose 1.61 percent to 15.65 rupees.
Lanka IOC fell 2.26 percent to 43.25 rupees.
John Keells Holdings Ltd rose 0.46 percent to 110 rupees, while Aitken Spence and Co Ltd rose 4.18 percent to 349 rupees, after sinking sharply in the wake of the tsunami.
Total market turnover was a provisional 107.6 million rupees.