Tha Mai (Thai: ท่าใหม่, pronounced [tʰâː màj]) is a district (amphoe) of Chanthaburi province, eastern Thailand.

The district is divided into 14 sub-districts (tambons), which are further subdivided into 124 villages (mubans).

There are three sub-district municipalities (thesaban tambons): Tha Mai covers tambons Tha Mai and Yai Ra, Noen Sung covers parts of tambon Khao Wua and Khao Baisi, and Nong Khla covers parts of Thung Bencha.

Missing numbers belong to tambons which now form districts Kaeng Hang Maeo and Na Yai Am.

Tha Mai is regarded as a small district that is quiet and people have a traditional way of life.