The benchmark Korea Composite Stock Price Index lost 5.29 points, or 0.22 percent, to close at 2,360.18. Trade volume was moderate at 315 million shares worth 5.8 trillion won ($5.3 billion), with losers far outnumbering gainers 546 to 253.
Institutional buyers purchased a net 41.2 billion won worth of shares on the main exchange, while foreign and individual investors offloaded a net 30.1 billion won and 60.6 billion won, respectively.
The Seoul index had opened a tad lower despite overnight Wall Street gains. On Tuesday (local time), the major Wall Street indexes hit record highs on Apple's new iPhone launch, with the S&P 500 Index adding 0.2 percent and the tech-heavy Nasdaq composite index gaining 0.12 percent.
"The overnight US gains and Apple's new product had a positive impact on the local stock market," said Seo Sang-young, a researcher at Kiwoom Securities Co. "Yet, a profit-taking stance among foreign investors kept the index from further going up."
Large caps on the Seoul bourse closed mixed.
Tech shares ended higher, with top cap Samsung Electronics adding 0.04 percent to close at 2,481,000 won and its smaller rival LG jumping 5.3 percent to 87,400 won. SK hynix, a major chipmaker, advanced 1.34 percent to 75,700 won after hitting an intraday high of 77,400 won.
Auto stocks closed bearish, with leading automaker Hyundai Motor losing 1.47 percent to 134,000 won and its sister company, Kia Motors, shedding 2.89 percent to 30,250 won. Auto parts maker Hyundai Mobis decreased 1.83 percent to 215,000 won.
Chemical shares closed mixed. LG Chem, the country's top chemical firm, gained 4.49 percent to a record high of 407,500 won, and No. 2 player Lotte Chemical was down 0.24 percent to 414,000 won.
Leading game publisher NCsoft jumped 3.62 percent to close at a record high of 472,500 won on the back of huge popularity of its mobile game "Lineage M."
The local currency closed at 1,128.5 won against the US dollar, unchanged from Tuesday's close.
Bond prices, which move inversely to yields, ended higher. The yield on three-year Treasurys shed 1.1 basis point to 1.742 percent and the return on the benchmark five-year government bonds lost 0.6 basis point to 1.949 percent. (Yonhap)