To simply and profitably obtain the subject compound in a high yield by reacting a dialkyl-arylidene-cycloalkanone compound with an alkyl halide in the presence of a metal halide and a tertiary alcohol.

A 2-alkyl-arylidene-cycloalkanone compound of formula I [A is -(CH2)x- [(x) is 1, 2, 3]; R2 is a 1-4C alkyl, a 3-7C cycloalkyl; R3 to R5 are each H, a 1-4C alkyl, a 3-7C cycloalkyl; X is a halogen, cyano, nitro, a 1-4C alkyl; a 1-4C halogenoalkyl, etc.; (n) is an integer of 0, 1-5] is reacted with (B) an alkyl halide (especially preferably methyl chloride or methyl bromide) in the presence of a metal hydroxide and a tertiary alcohol to obtain a 2,2- dialkyl-arylidene-cycloalkanone compound of formula II (R1 is the same as R2). The compound of the component A includes 2-methyl-5-(4-chlorobenzylidene)- cyclopentanone.