The index fell for the second day running after dropping 0.68 per cent on Monday.
In the morning session, Krungsri Securities forecast the index on Tuesday would move between 1,610 and 1,630 points despite rising oil and coal prices in line with global economic recovery.
It said the index also gained positive sentiment from Thailand’s move to lift Covid-19 restrictions on more businesses to get the economy running.
"However, uncertainty over the domestic floods and a weakening baht would trigger outflows of foreign funds, resulting in pressure on the index," Krungsri Securities added.
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The 10 stocks with the highest trade value today were KBANK, PTT, PTTGC, PTTEP, SCB, TRUE, BANPU, BBL, TOP and SCC.
Other Asian indices were mixed:
Japan's Nikkei Index closed at 30,183.96, down 56.10 points or 0.19 per cent.
China's Shanghai SE Composite Index closed at 3,602.22, up 19.39 points or 0.54 per cent, while the Shenzhen SE Component Index closed at 14,313.82, down 30.46 points or 0.21 per cent.
Hong Kong's Hang Seng Index closed at 24,500.39, up 291.61 points or 1.20 per cent.
South Korea's KOSPI closed at 3,097.92, down 35.72 points or 1.14 per cent.
Taiwan's TAIEX closed at 17,181.44, down 132.33 points or 0.76 per cent.