South Korean stocks advanced for a third straight session on Wednesday ahead of the US Federal Reserve's rate-decision meeting slated for later this week. The Korean won fell against the US dollar.

The benchmark Korea Composite Stock Price Index (KOSPI) edged up 2.57 points, or 0.11 percent, to close at 2,415.53 points.

Trading volume was moderate at about 324 million shares worth some 6.9 trillion won (US$5.3 billion), with gainers outnumbering losers 492 to 336.

Institutions sold a net 55 billion won and foreigners offloaded 118 billion won, while retail investors bought 212 billion won.

After a lackluster start, trading was weak with widespread expectations that the US Fed may deliver another sharp interest hike this week.

The key stock index rebounded, led by bio advances.

The US Fed is set to announce the results of its two-day monetary meeting results Thursday (Korean time).

Overnight, the US stock market closed lower. The Dow Jones Industrial Average fell 0.71 percent, and the tech-heavy Nasdaq Composite decreased 1.87 percent.

"In the local financial markets, investors seem to be waiting for the (Fed's policy) guidance about the rate hikes from the FOMC meeting," said DS Investment & Securities analyst Yang Hye-jeong.

In Seoul, market behemoth Samsung Electronics added 0.16 percent to 61,800 won, while No. 2 chipmaker SK hynix declined 0.5 percent to 100,000 won.

Bio heavyweight Samsung Biologics advanced 1.57 percent to 841,000 won, with Celltrion increasing 1.88 percent to 189,500 won.

Battery giant LG Energy Solution slipped 0.13 percent to 393,500 won, and chemical giant LG Chem lost 0.35 percent to 565,000 won.

Leading carmaker Hyundai Motor closed unchanged at 196,000 won, and internet portal operator Naver gained 0.41 percent to 246,000 won.

The local currency closed at 1,313.3 won against the US dollar, down 5.7 won from the previous session's close.