A survey of the amphibians and reptiles of Reserva Natural Absoluta Cabo Blanco (RNACB), Puntarenas, Costa Rica was conducted from May to August 2003. Thirteen amphibian and 19 reptile species were found within the RNACB boundaries. Twenty-two of these species were not previously recorded from the lower Nicoya Peninsula and for seven, this locality represents the southernmost extension of their range. One additional amphibian and three reptile species are known from the area based on literature review and examination of museum collections. However, interviews with locals indicate that up to nine other reptile species could be present in the reserve. I observed all but one amphibian species at Laguna Balsitas and at least eight species utilize the lagoon for reproduction. The lagoon is also notable for its population of Kinosternon scorpioides. This study will provide a baseline for further research in the reserve.