A process for producing optically active (R)-amino compounds which comprises treating an aralkyl alkyl ketone compound (the amino receptor) coexisting with a racemic or (R)-amino compound (the amino donor) with an (R)-specific transaminase produced by a microorganism belonging to the genus Arthrobacter and thus effecting stereoselective transamination. This process makes it possible to facilitate the production in a high yield of optically active (R)-amino compounds, etc., having aryl, etc. at the 1-position which have been difficult to synthesize by the conventional techniques.