The (Roman Catholic) Diocese of Nakhon Sawan (Dioecesis Nakhonsauanensis, Thai: สังฆมณฑลนครสวรรค์) is located in central Thailand.

The diocese covers an area of 93,547 km2, covering 13 provinces - Chainat, Kamphaeng Phet, Lopburi, Nakhon Sawan, Saraburi, Sukhothai, Tak, Uthai Thani, Uttaradit.

As of 2001, of the 8.2 million citizen 9,237 are member of the Catholic Church.

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 (15°41′37″N 100°7′13″E / 15.69361°N 100.12028°E / 15.69361; 100.12028).