The benchmark Korea Composite Price Index rose 9.44 points, or 0.40 percent, to close at 2,375.84. Trade volume was moderate at 290.54 million shares worth 4.59 trillion won ($4.07 billion), with gainers outnumbering losers 428 to 372.
Institutional investors bought a net 120 billion won. Foreigners bought stocks worth 14 billion won, extending their buying to a third straight session.
The KOSPI index is widely expected to move in a tight range this week as investors await cues from the US Federal Reserve's annual economic policy symposium in Jackson Hole, Wyoming.
Large-cap stocks traded mixed across the board, with bellwether Samsung Electronics rising 0.08 percent to 2,376,000 won, but top carmaker Hyundai Motor falling 2.05 percent to 143,500 won.
The country's No. 2 chipmaker SK hynix Inc. climbed 0.15 percent to 68,100 won, and leading steelmaker POSCO declined 0.15 percent to 330,000 won.
The local currency closed at 1,127.90 won against the US dollar, up 3.90 won from Wednesday's close.
Bond prices, which move inversely to yields, ended mixed. The yield on three-year Treasurys rose 0.4 basis point to 1.801 percent but the return on the benchmark five-year government bond fell 0.4 basis point to 1.801 percent. (Yonhap)