The Diocese of Nakhon Sawan (Dioecesis Nakhonsauanensis, ) in central Thailand is a Latin Catholic suffragan diocese of the Archdiocese of Bangkok.
The diocese covers an area of 93,547 km<sup>2</sup>, covering 13 provinces - Chainat, Kamphaeng Phet, Lopburi, Nakhon Sawan, Saraburi, Sukhothai, Tak, Uthai Thani, Uttaradit.
As of 2001, of the 8.2 million citizens, 9,237 are Catholics. It is divided into 28 parishes, having 27 priests altogether.
The diocese was erected on February 9, 1967, when it was split off from the archdiocese of Bangkok.
The St. Anna Cathedral is located in downtown Nakhon Sawan ().