Caja de Muertos Nature Reserve (Spanish: Reserva Natural Isla de Caja de Muertos) is a nature reserve in southern Puerto Rico consisting of the islands of Caja de Muertos, Cayo Morrillito, , and their surrounding reefs and waters in the Caribbean Sea. This nature reserve was founded on January 2, 1980, by the Puerto Rico Planning Board (Junta de Planificación) as recommended by the Puerto Rico Department of Natural and Environmental Resources (Departamento de Recursos Naturales y Ambientales de Puerto Rico, DRNA) with the purpose of preserving the subtropical dry forest ecosystems found within these islands, some important sea turtle nesting sites, and the marine habitats found on their surrounding reefs and waters.