The origin of the Ounalom Pagoda can be traced to as far back as the 15th Century. It was built in 1422 by King Ponyea Yat, the last king of the Khmer empire. It is one of the five original monasteries in Phnom Penh that King Ponhea Yat had built, the pagoda founded in the 1440's in Phnom Penh when the City was made the Kingdom's capital.
This pagoda comprises of the country's religious establishment. It is here where the top monk of the nation resides. In the earlier years, this pagoda served as the library of the Buddhist Institute. At that time, this place has cumulated about 30,000 titles.
In the recent times, this old institute has been re-positioned to more spacious areas on the Sihanouk Boulevard. The most important and eminent attribute related to this wat or pagoda is a hair from Buddha's eyebrow which is referred to as 'ounalom'. At present, it has been conserved carefully in a building situated behind the main wat of the Ounalom Pagoda.
But the Khmer Rouge from 1975 to 1979 caused serious sabotage to the Wat’s valuable cultural artifacts and book collection as well as taking away the lives of the majority of monks who lived there during this period.
Nevertheless, Buddha’s eyebrow miraculously survived and is still the focal point of the Wat. Later, Wat Ounalom provisionally housed the Buddhist Institute, prior to its shifting to a much larger area on the Sihanouk Boulevard in 1999.