The won closed up W7.8 against the U.S. dollar on Wednesday at W1,022.5, the highest since Aug. 7, 2008.
Korean exporters cashed in their holdings of the weakening dollar as the nation achieved a current account surplus for the 25th-straight month.
Dealers expect the won to strengthen above W1,000 in the second half of this year.
The won had traded between W1,060 and W1,070 until breaching the W1,050 mark on April 9. It has risen 3.2 percent against the greenback over the last month alone, the biggest margin among the currencies of the world's top 30 exporting countries.