A new species, Mucuna japira A. M. G. Azevedo, Agostini & Sazima, is described from Brazil. It has features similar to M. sloanei Fawc. & Rendle, but has pseudo‐racemose inflorescences and the standard petal measures ¾ of the length of the keel, whereas M. sloanei has umbellate inflorescences and the standard petal measures ½ of the length of the keel. This new species is restricted to the Atlantic forest of coastal São Paulo, Southeastern Brazil. A key to Brazilian species is provided.