The Stock Exchange of Thailand ended four consecutive sessions of gains, while Indonesian shares dropped on Monday amid ongoing presidential elections in Southeast Asia's largest economy.
The SET index closed 6.70 points or 0.38% to 1,749.42, in turnover of 44 billion baht. Thai shares snapped four consecutive sessions of gains, weighed down by materials and industrials. Siam Cement Plc was the top drag with a drop of 1.3%.
Indonesian President Joko Widodo launched his re-election campaign on Friday, looking to win over big blocs of millennial and Muslim voters as the country sails into choppy waters.
The Jakarta SE Composite Index closed lower for the first time in four sessions, dragged by consumer stocks and financials. Astra International declined 2.4%, while Bank Negara Indonesia (Persero) closed 3.6% lower.
Investor sentiment was also hit as broader Asian peers registered losses, after China decided to scrap plans to hold discussions with the United States, accusing it of engaging in "trade bullyism".
"The rebound in risk appetite witnessed last week we think may be done, with investors likely sidelined pending headline risks from Sino-US trade talks," OCBC said in a note to clients.
The US and China imposed tariffs on each other's goods on Monday, relentlessly pursuing an increasingly bitter trade dispute that is expected to hurt global economic growth.
Meanwhile, a Reuters poll showed Indonesia's central bank is widely expected to raise its benchmark interest rate for the fifth time since mid-May on Thursday, hours after an anticipated third rate hike this year by the US Federal Reserve.
Malaysian shares fell for the first time in four sessions, with power provider Tenaga Nasional leading the decline, down over 1%.
Singapore shares erased earlier gains and closed slightly higher, marking their fourth straight session in the black, as upbeat bank and real estate stocks countered weak consumer discretionary and industrial counters.
United Overseas Bank was the top boost with a rise of 1.4%, while Genting Singapore Ltd was among the biggest drags.
The city-state's core inflation gauge in August rose 1.9% from a year earlier, unchanged from July. The median forecast in a Reuters poll was for a 2% rise.
Philippine stocks advanced 0.7%, helped by financials and industrials. Bank of the Philippine Islands was the top boost with a 5.1% jump.
Real estate and utility stocks helped Vietnam shares finish at their strongest level in more than three months.