Shares in refiners fell, led by the biggest Thai Oil Pcl and PTT Global Chemical Pcl, on concerns over the impact of falling oil prices on their earnings for the April-June quarter.
Thai Oil shares fell 3.3 percent to 59.5 baht while PTT Global shares dropped 3.4 percent to 57.25 baht, underperforming the energy subindex and the broader stock market , which were down 1 percent and 0.2 percent respectively.
"In the second quarter, refinery sector earnings are likely to be dragged down by a sharp fall in oil prices. Monthly average Dubai crude oil prices have kept falling every month since end-March," broker Phillip Securities said in a report.
The broker, which rated refiners at 'neutral', said the weakening earnings outlook had already been priced in by the market.
1529 (0829 GMT) (Reporting by Viparat Jantraprap in Bangkok; firstname.lastname@example.org)