The Stock Exchange of Thailand index closed lower, while other Southeast Asian markets ended mixed on Wednesday.
Broader investor sentiment was low as US threats of tariffs on an additional US$200 billion worth of Chinese goods pushed the world's two biggest economies ever closer to a full-scale trade war.
The SET index closed 6.97 points or 0.42% lower to close at 1,636.63, in trade worth 44.49 billion baht. Thai shares snapped three consecutive sessions of gains. PTT Plc fell 0.5% and Airports of Thailand Plc dropped 1.2%.
Singapore's FTSE Straits Times Index closed 0.8% lower, with Oversea-Chinese Banking Corp and DBS Group Holdings shedding 2 percent and 1.1%, respectively.
"If overall regional and China-centric trade flows decline, the Singapore economy will likely take a hit due to its dependence on trade and manufacturing activities," OCBC Bank said in a note.
Vietnam shares extended losses into a third session with financial services provider Vietcombank closing 3.6% lower.
Philippine shares rose 1.4% to a one-week closing high with industrials at the helm.
"Despite Philippine's trade exposure to China and US being relatively high, given that a majority of the country's growth is fuelled by domestic consumption, it is less susceptible to trade fluctuations as compared to other Asean countries," OCBC Bank added.
SM Investments climbed 4.2%, while Ayala Land gained 2.1%.
Malaysian shares erased early losses to close marginally higher.
Earlier in the day, the central bank kept its key interest rate at 3.25% at its first policy meeting under the newly appointed central bank governor.
Indonesian shares closed 0.2% higher with Astra International being the biggest boost.