2018 South Korean by-elections

The following Members of National Assembly lost or resigned from their seats:

• Seoul Nowon C District: Ahn Cheol-soo (People's), due to Ahn's candidacy for the President of South Korea.
• Seoul Songpa B District: Choi Myung-gil (People's), due to Choi's violation of the Public Official Election Act.
• Busan Haeundae B District: Bae Duk-kwang (Liberty Korea), due to Bae's resignation from the National Assembly.
• Incheon Namdong A District: Park Nam-choon (Democratic), due to Park's resignation from the National Assembly, to run 2018 Incheon mayoral election.
• Gwangju Seo A District: Song Gi-seok (People's), due to Song's violation of the Public Official Election Act and embezzlement.
• Ulsan Buk District: Yoon Jong-oh (Minjung), due to Yoon's violation of the Public Official Election Act.
• North Chungcheong Jecheon-Danyang District: Kwon Suk-chang (Liberty Korea),due to Kwok's violation of the Public Official Election Act.
• South Chungcheong Cheonan A District: Park Chan-woo (Liberty Korea), due to Park's violation of the Public Official Election Act.
• South Chungcheong Cheonan C District: Yang Seung-cho (Democratic), due to Yang's resignation from the National Assembly, to run 2018 South Chungcheong Province gubernatorial election.
• South Jeolla Yeongam–Muan–Sinan District: Park Jun-yeong (Democracy and Peace), due to Park's violation of the Public Official Election Act.
• North Gyeongsang Gimcheon District: Lee Cheol-woo (Liberty Korea), due to Lee's resignation from the National Assembly, to run 2018 North Gyeongsang Province gubernatorial election.
• South Gyeongsang Gimhae B District: Kim Kyung-soo (Democratic), due to Kim's resignation from the National Assembly, to run 2018 South Gyeongsang Province gubernatorial election.