Cathedral of the Immaculate Conception in Chanthaburi holds the distinction of being the biggest Roman Catholic church building in Thailand. It is the mother church of the Diocese of Chanthaburi, which covers the provinces of Chanthaburi, Chonburi, Prachinburi, Rayong, Sa Kaeo and Trat.
The Cathedral of the Immaculate Conception was built in the Gothic style in 1909. It is located along Chanthanimit road, on the left bank of the Chanthaburi River. The cathedral stands on the site of the first missionary chapel which was built there in 1711. It grew a few times when the parish was enlarged by the infusion of Vietnamese Christians who fled religious persecution in the home coountry seeking refuge in Thailand.