Wat Noi, or the Little Monastery, is a defunct temple situated on Ayutthaya's city island outside the Historical Park in the Pratu Chai Sub-district.

The monastery shows on a 19th-century map by an unknown surveyor. Wat Noi was situated south of Wat Pa Sak, on the south side of the old road linking the Sing Bridge with the Pratu Talat Jin Bridge. This road does not exist anymore today. The map indicates the presence of a chedi. The temple was between Khlong Pratu Jin (1) and Khlong Pratu Thep Mi (2).

In the old documents, there is a road named after the monastery, namely Wat Noi Village Road. On this road and close to Pratu Jin (the Chinese Gate on Khlong Pratu Jin), the Chinese Gate Market sells brass-plated and mercury-plated goods. [2]

Phraya Boran Rachathanin (PBR) shows a structure called ‘Tuk Rap Khaek Mueang Farangset’ (ตึกรับแขคเมืองฝรั่งเศส) in the area located between the two canals and below the old road. Phraya Boran (1871-1936 CE) was the Superintendent Commissioner of Monthon Ayutthaya from 1925 till 1929 CE but occupied important functions since 1896 CE in Monthon Ayutthaya. Tuk Rap Khaek Mueang Farangset means the "building to receive the guests of France", and it was the place where the first French Embassy was received. The building belonged to an influential Persian Minister at that time. (3)

Whether both structures were the same will likely remain unknown as remnants are lost in time.

Historical data about the monastery and its construction are unknown.

Wat Noi must have been located in the approximative geographical coordinates: 14° 20' 55.06" N, 100° 34' 6.88" E.
(1) Khlong Pratu Jin, or the Canal of the Chinese Gate, is part of a waterway running through the middle of Ayutthaya from north to south. The canal ran from the Chikun Bridge to the Chinese Gate (Pratu Jin), one of the eleven water gates at that time and was an extension of Khlong Pratu Khao Pluak. The canal was a shortcut through the oxbow of the Lopburi River and connected the old Lopburi River, present Khlong Mueang in the north with - what is today - the Chao Phraya River in the south. The canal could have been the eastern defence moat of the initial city.(2) Khlong Pratu Thep Mi was situated on Ayutthaya's city island outside the Historical Park in Pratu Chai sub-district. The north-south running canal had its mouth at the old Lopburi River opposite the mouth of Khlong Phraya Phan, leading to Wat Phraya Kong and Wat Phraya Phan. The canal was fed by the waters of Bueng Phra Ram, which in its turn was filled by the waters of the Lopburi River via the Lam Khu Pak Sra. The canal passed the fortified city wall at the Thep Mi Gate, also known as the Khao Semi Gate, a large watergate. The canal has been filled up after the fall of Ayutthaya (1767 CE), and only a few traces of the waterway are left today.
(3) Guy Tachard wrote: "The King of Siam had ordered a stately House to be built for the Ambassador but seeing it was not yet finished, and that there was no delay to be made because of the Season that pressed his return, Monsieur Constance went himself and pitched upon the fairest and most commodious House of the Town, which belonged to a great Mandarin, a Persian by Nation, and had it splendidly furnished". [1]
[1] Tachard, Guy. A Relation of the Voyage to Siam, performed by Six Jesuits sent by the French King to the Indies and China in the Year 1685. [1688] Bangkok: White Orchid Press, 1981. p. 148.
[2] Baker, Chris (2011). Before Ayutthaya Fell: Economic Life in an Industrious Society. Markets and Production in the City of Ayutthaya before 1767: Translation and Analysis of Part of the Description of Ayutthaya. Journal of the Siam Society. Vol. 99.