The local currency stood at 1,061.7 against the dollar at the end of onshore trade, compared with Tuesday's local close at 1,063.0.
Worries over possible government intervention had kept trading subdued earlier in the day with no major cues to influence investors. Dealers had suspected on Monday that local authorities bought at least $1 billion in dollars to stem the won's rally.
However, steady supply of dollars from local exporters and offshore players' bets on the won eventually pushed the local currency higher towards the end of Wednesday's trading.
"Nobody except the local authorities are bidding up the dollar, so the degree of their interventions is determining where the won's resistance level is," a currency dealer said, adding that 1,060 will serve as a key level for the coming session.
Dealers suspected that local authorities stepped in throughout Wednesday in an attempt to ease the won's rise.
The benchmark Korea Composite Stock Price Index ended down 0.3 percent at 1,991.81. Foreigners were net buyers of 4.8 billion won ($4.52 million) worth of local shares on Wednesday.
Local bonds edged down on Wednesday as investors were already in wait-and-see mode ahead of the Bank of Korea's policy rate decision on Friday.
A Reuters poll showed 17 out of 22 analysts predict that the central bank will hold rates steady for a third straight month at 2.75 percent but keep the door open to a rate cut soon.
March futures on three-year treasury bonds ended down 0.02 points at 106.29.
Yield on the benchmark five-year treasury bonds were unchanged from Tuesday's close, while yield on the three-year treasury bonds ended up by one basis point.