The benchmark Korea Composite Stock Price Index rose 1.31 points, or 0.06 percent, to 2,366.05 as of 11:15 a.m.
On Tuesday, North Korea lobbed a ballistic missile over Japan in a move that could pose serious security challenges for Northeast Asia.
Market heavyweights traded mixed, with market kingpin Samsung Electronics down 0.17 percent.
SK hynix, a major chipmaker, rose 1.18 percent, and POSCO, the No. 1 steelmaker, remained flat.
Naver, the country's top Internet portal operator, backtracked 0.77 percent, while Hyundai Motor, the No. 1 automaker, dropped 1.04 percent on concerns that its sales in China may face a protracted slump over a diplomatic row over the deployment of a US missile defense system here.
LG Chem, the country's top chemical firm, advanced 3.66 percent on hopes that its electricity vehicle battery business will improve.
The local currency was trading at 1,121.85 won against the US dollar, up 4.15 won from the previous session's close. (Yonhap)