PURPOSE: To advantageously obtain ketimine useful as an intermediate of an antidepressant by condensing naphthalene corresponding to an objective compd. with methylamine in a specific solvent by using a molecular sieve possible to hydrate having a specific pore size as a catalyst.

CONSTITUTION: A molecular sieve possible to hydrate having a pore size of at least 3 is used as a catalyst in order to effectively remove water from a reaction mixture until the formation of an objective compd. is substantially completed and 4-(3,4'dichlorophenyl)-3,4-dihydro-1(2H)-naphthalenone is brought into contact with an excessive mol amt. with respect to the compd. of methylamine in the presence of the catalyst in an aprotic org. solvent inactive to reaction at about 20-100°C under pressure of about 1-10 atm to easily obtain N-[4-(3,4-dichlorophenyl)-3,4-dihydro-1(2H)-naphthalenidene]methanamine in a pure form in high yield.