Loss of Korean Nationality from Acquisition of a Foreign Nationality 
Loss of Korean Nationality- A national of the Republic of Korea who has voluntarily acquired a foreign nationality loses his or her Korean nationality when the foreign nationality is acquired (Paragraph 1 of Article 15 of the Nationality Act).
- A national of the Republic of Korea who falls under any of the following categories and does not declare an intention to retain his or her Korean nationality to the Minister of Justice within 6 months after acquiring a foreign nationality loses his or her Korean nationality retroactively from the time of acquisition of the foreign nationality (Paragraph 2 of Article 15 of the Nationality Act).
· National of the Republic of Korea who married a foreign national and acquired the spouse's nationality
· National of the Republic of Korea who was adopted by a foreign national and acquired the nationality of the foster father or mother
· National of the Republic of Korea who, by filiation to a father or mother who is a foreign national, acquired the nationality of the father or mother
· The spouse or a minor child of an individual who lost his or her Korean nationality after acquiring a foreign nationality, who in accordance with the law of the foreign country acquired the foreign nationality
- If an individual loses his or her Korean nationality by acquiring a foreign nationality but the date of acquisition of the foreign nationality is not known, it will be assumed to be the date on which the foreign passport used by the individual was initially issued (Paragraph 3 of Article 15 of the Nationality Act).
Declaration of Loss of Nationality- With the exception of cases in which the individual has declared a renunciation of Korean nationality, an individual who has lost his or her Korean nationality must officially declare a loss of Korean nationality by submitting the following documents to the head of an immigration office or its branch office (hereinafter referred to as the "head of an immigration office”, etc.") (Article 16(1) and 26 of the Nationality Act, Article 20(1) and Article 29 Subparagraph 7 of the Enforcement Decree of the Nationality Act and Article 14 and Attached Form 10 of the Enforcement Rule of the Nationality Act).
1. Declaration of loss of Korean nationality
2. Certificate of records of family relations
3. Document corroborating the reason and date of loss of Korean nationality (if a foreign nationality was acquired, a document corroborating the reason and date of acquisition of a foreign nationality) and a copy of foreign passport
Change of Rights from Loss of Korean Nationality- An individual who has lost his or her Korean nationality cannot claim the rights exclusive to Korean nationals and must transfer to a Korean national within 3 years any rights which he or she acquired while a Korean national unless specified otherwise by a law related to such rights (Article 18 of the Nationality Act).