The (Roman Catholic) Diocese of Chanthaburi (Dioecesis Chanthaburiensis, Thai: สังฆมณฑลจันทบุรี) is located in eastern central Thailand.

The diocese covers an area of 34,000 km2, covering the provinces - Chanthaburi, Chonburi, Prachinburi, Rayong, Sa Kaeo and Trat, as well as the parts east of the Bang Pa Kong River in Chachoengsao, and Nakhon Nayok except the district Ban Na.

[citation needed] The Cathedral of the Immaculate Conception (Thai: อาสนวิหารพระนางมารีอาปฏิสนธินิรมล) 12°36′33.5″N 102°7′7″E / 12.609306°N 102.11861°E / 12.609306; 102.11861 is the largest church of Thailand.

After being enlarged and rebuilt four times during the nineteenth century, especially due to the immigration of Vietnamese Christian fleeing religious persecution in the home country.

During World War II the spires were taken down to make the church a less obvious navigational aid to allied bombers; they have since been replaced.