At noon, the dex was at 1,566.04 points.
Though rising to 1,595 points at the open, the index later fell later in the morning on sell-offs on big-cap stocks.
At the close, the index lost 19.25 points or 1.22 per cent, to 1,562.07, on turnover of Bt75.6 billion.
During the first four days of this week, foreign net-sells totalled Bt15 billion. Today, they returned to be net-buyers, with net purchases of Bt351 million.
Asia Plus Securities said in a research note that based on technical analysis, the index could stage a rebound but it should not exceed 1,611 points. There is also a chance that the index could fall further to 1,450.
An analyst from KTB Securities (Thailand) foresees volatility throughout the day. If the index rebounds, profit-taking could pressure the market again, he said.
The index fell below the 1,600 points psychological level yesterday, as soon as the market opened, as investors were worried about the United States' premature exit from quantitative easing. The fears are eased today, as the US announced the 2.4 per cent economic growth rate for the first quarter - down from the 2.5 per cent target. The weekly jobless claims also rose by 10,000 to 354,000.
Tisco Securities expected the market to move sideway down today. The index should not rise beyond 1,600 points today, it said in a research note.