In the morning session, an analyst at Krungsri Securities expected the day's index to fluctuate between 1,440 and 1,465 points amid news that the European Union and Britain had reached a deal on Brexit, and Thailand had escaped a nationwide lockdown after the latest Covid-19 outbreak.
However, the index would come under pressure from the decline in fund flows over the Christmas and New Year period, said the analyst.
The 10 stocks with the highest trade value today were DELTA, AEONTS, KEX, IVL, SA, IRPC, BANPU, SAWAD, PTTGC and MTC.
Other Asian indices were mixed:
Japan’s Nikkei Index closed at 26,656.61, down 11.74 points or 0.044 per cent.
China’s Shang Hai SE Composite Index closed at 3,396.56, up 33.45 points or 0.99 per cent, while Shenzhen SE Component Index closed at 14,017.06, up 101.48 points or 0.73 per cent.
Taiwan's TAIEX Index closed at 14,331.42, up 51.14 points or 0.36 per cent.
Hong Kong's Hang Seng Index and South Korea's KOSPI Index were closed for Christmas Day.