Werneria mertensiana is a species of toad in the family Bufonidae. It is found in western Cameroon (Mount Nlonako, Mount Manengouba, Mount Kala, possibly Western High Plateau) and possibly in the Obudu Plateau in Nigeria. The specific name mertensiana honours Robert Mertens, a German zoologist and herpetologist. Common name Mertens' smalltongue toad has been coined for it.