At 06:32 GMT, the KOSPI was down 9.77 points or 0.39 percent at 2,476.33. For the week, the index gained 0.9 percent, its second straight weekly gain.
The won was quoted at 1,067.3 per dollar on the onshore settlement platform, 0.6 percent lower than its previous close at 1,061.5. The currency gained 0.2 percent on a weekly basis.
In offshore trading, the won was quoted at 1,066.47 per US dollar, down 0.02 percent from the previous day, while in one-year non-deliverable forwards it was being transacted at 1,052.1 per dollar.
MSCI's broadest index of Asia-Pacific shares outside Japan was down 1.09 percent, while US stocks ended the previous session with losses. Japanese stocks weakened 0.13 percent.
The KOSPI is up around 0.8 percent so far this year, and up by 2.18 percent in the previous 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.
The trading volume during the session on the KOSPI index was 526,134,000 shares, and of the total traded issues of 887, the number of advancing shares was 525.
Foreigners were net sellers of 488,027 million won worth of shares.
In money and debt markets, June futures on three-year treasury bonds fell 0.06 points to 107.76.
The Korean 3-month Certificate of Deposit benchmark rate was quoted at 1.65 percent, while the benchmark 3-year Korean treasury bond yielded 2.201 percent, higher than the previous day's 2.20 percent.