Wat Ubosot, or the Monastery of the Ordination Hall, is a restored temple ruin located on the city island in the Pratu Chai Sub-district of Ayutthaya. The ruin is situated in the Somdet Phra Sri Nakharin Park, part of the Ayutthaya Historical Park.

Wat Ubosot lies west of Khlong Chakrai Yai, which has its mouth at the Chao Phraya River. Wat Jao Phram is on its north side, while Wat Jao Prap is on its south. Chedi Yai stands west of it.

The exact date of the temple's construction and its historical information are unknown.

The chedi features characteristics indicating its construction in the middle to late Ayutthaya period. The chedi is redented from its platform until the harmika. The high and redented square platform has a stairway on the south, leading to the chedi base. The chedi has a triple redented square base representing the three worlds or the Trai Phum. The three worlds are the sensual worlds, the form world, and the formless world, forming the Buddhist cosmology.

An ubosot or ordination hall stood in front of the chedi. This ubosot was altered in the late Ayutthaya period. The area has been up-levelled, and a new vihara has been built on top of the foundations of the ubosot.

The whole monastic area was before surrounded by a moat but can now easily be accessed.

Engelbert Kaempfer, a medical doctor working for the Dutch VOC (Verenigde Oost-Indische Compagnie), on his visit to Ayutthaya in June 1690 CE, indicates Wat Ubosot on his sketch.

The site shows on a map drafted in the 19th century and on Phraya Boran Rachathanin's map of 1926 CE. Wat Ubosot is indicated on the 19th-century map under the denomination Wat Bot, the same as on Phraya Boran Rachathanin's map drafted in 1926 CE.

The ruin of Wat Ubosot is in geographical coordinates: 14° 20' 35.03" N, 100° 33' 22.01" E.