Bang Khun Thian is one of the 50 districts (khet) located in Bangkok, Thailand. It serves as the southernmost district of the capital city.
The district is uniquely characterized by its geography, as it is the only district in Bangkok that borders the Bay of Bangkok. Its neighboring areas include Bang Bon, Chom Thong, and Thung Khru districts of Bangkok to the north; Phra Samut Chedi district of Samut Prakan province; and Mueang Samut Sakhon district of Samut Sakhon province.