Any foreign visitors wishing to enter the Republic of Korea must have a valid passport and obtain a Korean visa before coming. Some nationals who want to visit Korea temporarily are permitted to enter without a visa according to visa-exemption agreements, or in accordance with principles reciprocity or national interest.
Please visit http://www.mofat.go.kr/me/me_a006/me_b025/me06_01.jsp
(source: http://www.korea.net, Home > Korea > General > Visa&Immigration > Visa)