The rock art of the Pak Ou Caves in Luang Prabang, Lao PDR has been known for over 20 years, but to date a complete record of the site has not been made. This paper presents an inventory of the rock art found at site also known as the Cave of a Thousand Buddhas. Over 50 rock art elements, mostly paintings, have been found in the upper cave and on the cliff face overlooking the junction of the Mekong and Ou Rivers. The oldest red paintings depict domesticated buffalo, human figures and hand prints and bear similarities with other cliff-side rock art sites in highland Southeast Asia. Other paintings are associated with the conversion of the cave into a Buddhist shrine, which according to folk tradition was home to a powerful river spirit. The most recent paintings can be comfortably dated to the 20th century. The Pak Ou Caves are a significant Buddhist site today, but the variety of rock art suggests its significance predates the Buddhist period that began in the 15th century. The layered history of the site and its rock art attests to multiple episodes of site use and re-use, from possibly the Neolithic until today.