A process for conveniently and industrially producing an optically active α-methylcysteine derivative, which is useful as an intermediate of medicines and the like, from an inexpensive and readily available material is provided. The present invention relates to a process for producing a racemic or optically active α-methylcysteine derivative including a step of hydrolyzing a racemic or optically active N-carbamyl-α-methylcysteine derivative by treating with decarbamylase, and a process for producing an optically active α-methylcysteine derivative and an optically active N-carbamyl-α-methylcysteine derivative having a configuration opposite to that of the compound including a step of stereoselectively hydrolyzing a racemic N-carbamyl-α-methylcysteine derivative by treating with decarbamylase.