The Korean won edged down against the dollar and bond yields also fell.
At 06:32 GMT, the KOSPI was down 18.94 points, or 0.76 percent, at 2,475.03.
The won was quoted at 1,071.6 per dollar on the onshore settlement platform, 0.5 percent weaker than its previous close at 1,066.2.
In offshore trading, the won was quoted at 1,070.75 per US dollar, down 0.11 percent from the previous day, while in one-year non-deliverable forwards it was being transacted at 1,059.8 per dollar.
MSCI's broadest index of Asia-Pacific shares outside Japan was down 0.33 percent, after US stocks ended the previous session with mild gains. Japanese stocks weakened 0.9 percent.
The KOSPI is up around 1.1 percent so far this year, and up by 2.87 percent in the past 30 days.
The current price-to-earnings ratio is 12.10, the dividend yield is 1.28 percent and the market capitalisation is 1,242.04 trillion won ($1.16 trillion).
The trading volume during the session on the KOSPI index was 471,371,000 shares, and of the total traded issues of 887, the number of advancing shares was 275.
Foreigners were net sellers of 83,374 million won worth of shares.
The US dollar has risen 0.41 percent against the won this year. The won's high for the year is 1,056.67 per dollar on Jan. 14, 2018 and low is 1,098.4 on Feb. 6, 2018.
In money and debt markets, March futures on three-year treasury bonds rose 0.02 points to 107.85.
The Korean 3-month Certificate of Deposit benchmark rate was quoted at 1.65 percent, while the benchmark 3-year Korean treasury bond yielded 2.274 percent, lower than the previous day's 2.28 percent.