Prasat Khao Noi is situated on the premises of Wat Khao Noi Si Chompu in Khlong Nam Sai Sub-district of Aranyaprathet District about 1800 meters north of the Thai-Cambodian border. The ruin is located on top of Khao Noi (literally small mountain), a limestone mountain 147 meters above sea level.
The sanctuary is the earliest significant Khmer monument in Thailand. An inhumation burial was discovered at the site, suggesting a late prehistoric occupation prior to the construction of the temple. The Khao Noi Inscription, a sandstone rectangle bar with Pallava script found in situ, dates the brick sanctuary to 637 AD.
The Vaishnavite temple was restored in the 11th century AD and consisted of three east-oriented towers symbolising the Hindu Trimurti or 'three forms' Brahma-Vishnu-Maheswara. Today, only the central prang, extensively restored, remains while the other two prangs have only their foundation left. Many artefacts were found such as Saivite lingas and pedestals, an 11th century - iron coated with bronze - seal with a Sanskrit inscription, as well as five sandstone lintels in the Sambor Prei Kuk and Prei Kmeng (c. 635–700 AD) styles. The lintels in situ are replicas.
The original lintels and artefacts excavated at Khao Noi are kept and exhibited at the Prachin Buri National Museum. Prasat Khao Noi was registered as a national monument by the Fine Arts Department in 1935.

Source: onsite information