Seongdong District (Korean: 성동구; RR: Seongdong-gu) is one of the 25 districts which make up the city of Seoul, South Korea. It is situated on the north bank of the Han River. It is divided into 20 dong (neighbourhoods). The district is home to Hanyang University, one of the most prestigious universities in South Korea.

Seongdong District consists of 20 administrative dongs (haengjeong-dong, 행정동)

When Seoul was expanding outward on its size, many parts of Gyeonggi Province were merged to Seongdong District. However, due to its extraordinarily huge size, Seoul Metropolitan Government divided the district into 5 (Gangnam District, Gangdong District, Gwangjin District, Seongdong District, and Songpa District)^[1], and made Seongdong District cede some part of the district to Jung District. Yeongdeungpo District, Seodaemun District, Seongbuk District, and Dongdaemun District underwent similar changes.

Hanyang University, a prestigious university in South Korea, is located in Haengdang-dong and Sageun-dong.