A process for producing an optically active .gamma.-butyrolactone derivative represented by formula (II): ##STR1## wherein R.sup.1 represents an alkyl group having from 1 to 10 carbon atoms or a substituted or unsubstituted phenyl group; and * indicates an asymmetric carbon atom, is disclosed, comprising enantioselectively hydrogenating a .gamma.-keto acid or an ester thereof represented by formula (I): ##STR2## wherein R.sup.1 and * are as defined above; and R.sup.2 represents a hydrogen atom or a lower alkyl group, in the presence of an optically active ruthenium-phosphine complex. The compounds (I) can be obtained at high optical purity through simple operations and a reduced number of steps.