To obtain a 4,4'-di(N-alkylaniline) which is important as an curing agent for epoxy resins with industrial advantage in high yield, in high purity under mild reaction conditions by reductive alkylation of a 4,4'-dianiline with an aldehyde or ketone.

A compound of formula I (X is an alkylene; R2 and R3 are independently from each other H, a lower alkyl), for example, 4,4'- methylenedianiline is allowed to react with an aldehyde or ketone such as methyl ethyl ketone in the presence of a metallic catalyst under a hydrogen pressure to give a 4,4'-di(N-alkylaniline) of formula II (R1 is a lower alkyl), for example, 4,4'-methylenedi(N-sec-butylaniline).