The local currency was quoted at 1,083.0 against the dollar at the end of onshore trade, compared with 1,081.5 at the end of the Seoul session on Wednesday.
Dealers said the dollar was supported by importers' demands as well as banks deciding to build long positions on the US currency. Some players were also unwinding their shorts on the dollar once the won fell below the 1,083 mark.
"There was a fair amount of dollars being sold by exporters, but the euro was down and there was some short-covering by offshore players," a currency dealer said, adding that the won may undergo some correction given the strong resistance at the 1,080 mark.
Dealers also said fears about additional intervention by the local foreign-exchange authorities kept investors wary of increasing their bets on the currency.
"Still, the downward pressure on the dollar-won rate should remain intact, as the continued trade surplus will translate to ample supply of dollars," another dealer said.
The benchmark Korea Composite Stock Price Index ended up 0.1 percent at 1,949.62. Foreigners were net buyers of 215.6 billion won ($199.33 million) worth of local shares.
Local bonds rose, tracking US Treasuries. December futures on three-year treasury bonds ended up 0.05 point at 106.04.
Yields on the benchmark five-year treasury bonds fell one basis point, while the yield on three-year treasury bonds fell three basis points.