Gangdong-gu is located in the southeastern part of Seoul. It is adjoined to Guri-si, Gyeonggi-do in the north via Hangang(River), and to Gwangjin-gu in the west via Cheonhodaegyo. It is also next to Hanam-si, Gyeonggi-do in the east, and to Songpa-gu in the south via Gangdongdaero.
The area of Gangdong-gu is 4.1% of the total area of Seoul, 24.58㎢.
It is divided into 18 administrative districts(Dong).