The Stock Exchange of Thailand index ended marginally lower on Wednesday, snapping three straight sessions of gains, dragged by healthcare stocks.
Other Southeast Asian stock markets closed mixed, with Philippines rising nearly 3%, on rising optimism that talks between China and the United States could end a months-long trade war between the world's top two economies.
Chinese and US teams ended trade talks in Beijing on Wednesday that lasted longer than expected, with China's Foreign Ministry spokesman Lu Kang saying that the longer-than-expected negotiations suggested the countries were serious in talks.
"Sentiment across the region is improving due to the current talks between US and China, as investors are already buying back their positions in the market in expectation of positive results," said Rachelle Cruz, an analyst with AP Securities.
The SET index ended 1,590.50 at the close, easing 3.50 points or 0.22%, in turnover worth 46 billion baht.
Bangkok Dusit Medical Services Plc slumped two baht or 8.10% to close at 22.70, Bumrungrad Hospital Plc lost 16.50 baht or 8.57% to end at 176 baht, and Bangkok Chain Hospital Plc dropped 60 satang or 3.66% to 15.80 baht.
Healthcare stocks dropped after the government added medicine, medical supplies and medical services to its price control lists.
Philippine shares closed 2.8% higher, posting their sharpest gain since Sept 21, 2018 and their highest close in nine months, supported by industrials.
Conglomerates SM Investments Corp and JG Summit Holdings Inc advanced 6.1% and 5.9%, respectively.
"Foreign investors are coming back to the Philippine markets since the macro concerns have partly improved and the currency has strengthened against the dollar," said Cruz.
Foreign investors have invested a net US$75.53 million in equities so far this year after offloading $1.08 billion last year.
Last week, government data showed that inflation cooled more than expected in December. The market now awaits trade data for November due this week for further clues about the economy.
Singapore stocks climbed 1.1%, extending gains into a fourth session. Jardine Matheson Holdings Ltd, the index's largest company by market value, rose 1.9%, while DBS Group Holdings Ltd gained 1.4%.
Vietnam shares advanced over 1%, boosted by financial and real estate stocks. Joint Stock Commercial Bank for Investment and Development of Vietnam rose 3.1%, while Vincom Retail JSC gained 5.3%.