The Stock Exchange of Thailand closed up 0.13%, or 2.26 points, after briefing setting a record during intraday trade on Tuesday.
The index reached the high of 1,754.68 at 3.34pm before retreating. It closed at an all-time high 23 years ago on Jan 4, 1994, when it finished at 1,753.73.
Total trading value on Tuesday was 49 billion baht, with 6.3 billion shares changed hands.
The SET50 index advanced 0.04%, or 0.50 points, to 1,136.20 in trade worth 23.5 billion baht.
MAI fell 0.45%, or 2.44 points, to 539.73 in transactions worth 1.5 billion baht.
Institutional investors were net buyers of 1.1 billion baht worth of shares, followed by brokers (256.5 million baht). Foreigners sold 1.2 billion baht, followed by individual investors (501.5 million baht).
Year-to-date, institutional investors were net buyers of 99.6 billion baht, followed by brokers (19.4 billion baht). Retail investors were net sellers of 91.8 billion baht, followed by foreigners (19.4 billion baht).