The Cathedral of the Immaculate Conception (Thai: อาสนวิหารพระนางมารีอาปฏิสนธินิรมล) is the largest church of Thailand. A first missionary chapel was built at the site in 1711. After being enlarged and rebuilt four times during the nineteenth century, especially due to the immigration of Vietnamese Christian fleeing religious persecution in the homecountry.
In 1909 it was rebuilt in its current Gothic style. It is located at the Chanthanimit Road on the left bank of the Chanthaburi River. 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.