An optically active 1-(fluoro-, trifluoromethyl- or trifluoromethoxy-substituted phenyl)alkylamine N-monoalkyl derivative represented by the formula 4 is produced by a process including (a) reacting an optically active secondary amine, represented by the formula 1, with an alkylation agent R.sup.2--X, in the presence of a base, thereby converting the secondary amine into an optically active tertiary amine represented by the formula 3; and (b) subjecting the tertiary amine to a hydrogenolysis, thereby producing the N-monoalkyl derivative, ##STR00001## wherein R represents a fluorine atom, trifluoromethyl group or trifluoromethoxy group, n represents an integer of from 1 to 5, each of R.sup.1 and R.sup.2 independently represents an alkyl group having a carbon atom number of from 1 to 6, Me represents a methyl group, Ar represents a phenyl group or 1- or 2-naphthyl group, * represents a chiral carbon, and X represents a leaving group.