The benchmark Korea Composite Stock Price Index shed 5.7 points, or 0.24 percent, to close at 2,406.5. Trade volume was moderate at 270 million shares worth 5.5 trillion won ($4.85 billion), with losers overwhelming gainers 620 to 198.
The local bourse opened nearly flat after the US Federal Reserve hinted at the chance of a December rate hike but was knocked into negative terrain amid losses in market heavyweights.
"The decline was mainly driven by the losses in auto and steel shares," said analyst Seo Sang-young, a researcher at Kiwoom Securities Co.
After holding a two-day policy meeting, the Fed left interest rates unchanged and said it would begin reducing its bond portfolio starting next month.
Institutions and foreigners each dumped a net 200 billion won and 3 billion won worth of local stocks, while individuals scooped up a net 180 billion won.
No. 1 automaker Hyundai Motor lost 0.35 percent to end at 141,500 won, and its sister affiliate Kia Motors declined 2.39 percent to close at 30,600 won.
South Korea's top steelmaker POSCO surrendered 2.62 percent to 316,500 won, and No. 2 player Hyundai Steel was down 1.49 percent to 490,000 won.
Top market cap Samsung Electronics, meanwhile, gained 1.11 percent to end at a fresh record high of 2,640,000 won, after soaring to as high as 2,648,000 won at one point, amid a rosy outlook over its third quarter earnings.
SK hynix, a major chipmaker, also jumped 2.97 percent to close at a fresh all-time peak of 83,100 won, following Toshiba's decision to pick a Japan-US-South Korean consortium, which includes the SK affiliate, as a preferred bidder to buy its chip business unit.
Korea Aerospace Industries, the country's only aircraft maker, plunged 5.84 percent to finish at 143,500 won after its vice president was found dead in an apparent suicide earlier in the day amid a widening probe into a series of suspected irregularities at the company.
LG Chem, the country's top chemicals firm, gained 0.13 percent to close at 389,000 won, while leading cosmetics company AmorePacific retreated 0.8 percent to 249,000 won.
The local currency closed at 1,132.70 won against the US dollar, down 4.40 won from the previous session's close.
Bond prices, which move inversely to yields, ended mixed. The yield on three-year Treasurys gained 0.6 basis point to 1.781 percent and the return on the benchmark five-year government bonds shed 0.4 basis point to 1.979 percent. (Yonhap)