Ratchasan (, ) is a district (amphoe) in the central part of Chachoengsao province, central Thailand.
The area of Ratchasan was separated from Phanom Sarakham district and became a minor district (king amphoe) on 16 February 1977. It was upgraded to a full district on 4 July 1994.
Neighboring districts are (from the east clockwise): Phanom Sarakham, Plaeng Yao, and Bang Khla of Chachoengsao Province; and Ban Sang of Prachinburi province.
The important water resource is the Khlong Tha Lat.
Ratchasan is divided into three sub-districts (tambons), which are further subdivided into 31 administrative villages (mubans).
There are three sub-district administrative organizations (SAO) in the district:
Palmyrum is a local important industrial crop. Ratchasan is famous for its palm sap.