A new scansorial frog species of Mantidactylus (subgenus Phylacomantis) is described from Andasibe, a midaltitude locality in central, eastern Madagascar. The new species is similar to the sympatric Mantidactylus cornutus but differs by smaller size, presence of a chevron-like dorsal ridge, more distinct supraocular dermal spines, throat coloration, and advertisement call. Its discovery emphasizes the importance of midaltitude rain forests in central, eastern Madagascar as a center of anuran diversity.