This chapel is located to the south of Wat Phra Si Sanphet. A large bronze seated Buddha image (Phra Mongkhon Bophit) was originally enshrined outside the Grand Palace to the east. It could be dated to the 15th century and was originally intended to stand in the open air. Later, King Songtham commanded it to be transferred to the west, where it is currently enshrined and covered with a Mondop. In the reign of Phra Chao Sua, the top of the Mondop was burnt down by a fire due to a thunderbolt. The King then commanded that a new building be built in the form of a big sanctuary (Maha Wihan) to cover the image in lieu of the former Mondop. During the second fall of Ayutthaya, the building and the image were badly destroyed by fire. The present Viharn and Buddha image have been reconstructed and renovated. The open area located east of the Viharn was formerly Sanam Luang, where royal cremation ceremonies took place.
- Admission fee is 50 baht/person.