Ak Yum (Khmer: ប្រាសាទអកយំ) is an ancient temple in the Angkor region of Cambodia. The first structure on the site was a single-chamber brick sanctuary, probably constructed in the latter part of the 8th Century, scholars believe. Later it was remade into a larger stepped pyramid structure, with a base approximately 100 meters square.
The expansion probably took place in the early 9th Century during the reign of King Jayavarman II, who is widely recognized as the founder of the Khmer Empire. When the West Baray reservoir was built in the 11th Century, Ak Yum was partially buried by the southern dike. The site was excavated in the 1930s under the direction of archaeologist George Trouvé.