The Wat Mahathat is a Buddhist temple in Ayutthaya, central Thailand.

Wat Maha That or the Monastery of the Great Relic is located on the city island in the central part of Ayutthaya in Tha Wasukri sub-district. The temple is situated on the corner of the present Chikun Road and Naresuan Road. The monastery stood on the west bank of Khlong Pratu Khao Pluak, an important canal, which has been filled up somewhere in the early 20th century. In ancient times the temple was likely fully surrounded by canals and moats. The structure has been registered as a national historic site by the Fine Arts Department on 8 March 1935 and is part of the Ayutthaya World Heritage Historical Park.