Useful Info

Dual nationals must choose one nationality before reaching the age of 22 (or within 2 years from that point if they became dual nationals after turning 20). Dual nationals can receive citizen treatment before choosing their nationality. While receiving citizen treatment, they are exempt from obligations as foreigners, such as foreign resident registration, during their stay in Korea, and they must use a Republic of Korea passport when entering or exiting the Republic of Korea. A dual national not receiving citizen treatment must use a foreign passport for entry and exit and will be treated as a foreigner, including foreign resident registration and other stay procedures, during their stay in the Republic of Korea.
For a male dual national who wishes to renounce nationality after January 1 of the year he turns 18, he must have completed military service, been exempted from it, or been assigned to the second citizen service role.