The benchmark Korea Composite Stock Price Index (Kospi) fell 1.17 points, or 0.04 percent, to 3,124.59 points in the first 15 minutes of trading.
Stocks got off to a slow start, following North Korean state media saying Monday the communist state had successfully test-fired a new type of long-range cruise missile over the weekend.
Local stocks also came under selling pressure after US data pointed to rising inflation in the world's largest economy.
Top cap Samsung Electronics added 0.93 percent, and No. 2 chipmaker SK hynix advanced 0.48 percent.
Internet portal operator Naver moved down 0.37 percent, and pharmaceutical giant Samsung Biologics decreased 0.43 percent.
Leading chemical firm LG Chem gained 0.54 percent, but top automaker Hyundai Motor retreated 0.73 percent. No. 1 bank Kakao Bank shed 2.61 percent.
The local currency was trading at 1,172.6 won against the US dollar, down 3.5 won from the previous session's close. (Yonhap)