Krathum Baen (Thai: กระทุ่มแบน, pronounced [krā.tʰûm bɛ̄ːn]) is a district (amphoe) in the northern part of Samut Sakhon province, central Thailand.

Krathum Baen was a part of Mueang Samut Sakhon district.

In 1926 the government added Tambons Tha Mai, Bang Yang, Nong Kok Khai, and Om Noi of Sam Phran district, Nakhon Pathom province to the district.

Neighbouring districts are (from the north clockwise): Sam Phran of Nakhon Pathom province; Nong Khaem and Bang Bon of Bangkok; Mueang Samut Sakhon and Ban Phaeo of Samut Sakhon Province.

The important water resources are the Tha Chin river and Phasi Charoen canal.