The Korea Composite Stock Price Index took a nosedive on the first trading day of 2014 when the yen closed at less than W1,000 per 100 yen, the lowest in more than five years.
Concerns spread that Korea's key exports -- cars, electronics products and steel -- would lose their price competitiveness as rival Japanese products get cheaper.
Automobile shares were hit especially hard. Hyundai Motor fell 5.1 percent and parts-making affiliate Hyundai Mobis 4.9 percent, while Kia dropped 6.1 percent.
Samsung Electronics, the top listed company in terms of market capitalization, also fell 4.59 percent, but that was chiefly because of lower-than-expected fourth-quarter earnings.
The KOSPI closed down 2.2 percent at 1,967.2, with foreign investors selling W313.6 billion worth of Korean shares (US$1=W1,051).