The Stock Exchange of Thailand main index fell 1.12%, or 15.75 points, to 1,393.51 at noon on Thursday.
Total trading value was 28.23 billion baht, with 5.45 billion shares changed hands.
SET50 index fell 1.17%, or 10.64 points, to 900.22 in trade worth 15.09 billion baht.
MAI dropped 1.20%, or 7.25 points, to 594.55, in total transaction value of 977.13 million baht.