The index fell into negative territory following news that Finance Minister Predee Daochai had tendered his resignation less than a month after taking the post, citing health problems.
In the morning session, an analyst at Krungsri Securities expected the index to drop to between 1,300 and 1,305 due to lack of positive sentiments to boost investment.
"Also, the index would be under pressure from the slump in the US Dow Jones Index, which fell sharply by 224 points after China implemented new rules on technology exports," the analyst said.
"This negative sentiment caused [China’s] ByteDance to request approval from [Beijing] before selling its TikTok business to the US, resulting in mass sell-offs in stocks which had aimed to buy the TikTok business, such as Microsoft, Walmart and Oracle."
The analyst added that foreign investors' mass sell-off of Thai shares also pressured the index.
The 10 stocks with the highest trade value today were CPF, BAM, KBANK, CPALL, MINT, SCC, PTT, BBL, ICHI and AOT.
As of 4.30pm, the price of oil rose by US$0.45 or 1.06 per cent to $43.06 per barrel, while gold rose by $16.50 or 0.83 per cent, to $1,995.10 per ounce.
Other Asian indices were mixed:
Japan’s Nikkei Index closed at 23,138.07, down 1.69 points or 0.0073 per cent.
China’s Shang Hai SE Composite Index closed at 3,410.61, up 14.93 points or 0.44 per cent, while the Shenzhen SE Component Index closed at 13,849.66, up 91.43 points or 0.66 per cent.
Hong Kong’s Hang Seng Index closed at 25,184.85, up 7.80 points or 0.031 per cent.
South Korea’s KOSPI Index closed at 2,349.55, up 23.38 points or 1.01 per cent.
Taiwan’s TAIEX Index closed at 12,703.28, up 111.83 points or 0.89 per cent.