We report a new locality for Osteocephalus mimeticus from southeast Peru which is the first record for the Madre de Dios region and a first record for Manu Biosphere Reserve. Combined with data from recent literature it also supposes a range extension of ~210 km to the southeast. We provide notes related to the environment in which this species has been found, along with photos of different individuals. We have produced a potential range map for the species, derived from known confirmed localities in which O. mimeticus has been previously found, combined with environmental and climatic data.