To profitably obtain the subject diastereomer compound useful as a medicine, an agrochemical, their intermediate, etc., in a high yield by reacting a specific styrene oxide with the halogenomagnesium complex of a specific optically active primary amine.

This method for producing an optically active aminoalcohol comprises reacting (A) a compound of formula I (R1 is H, F, Cl, Br, methyl, methoxy; * exhibits an asymmetric carbon) with (B) a compound of formula II (R2, R3 are each H, methyl, ethyl, methoxy, ethoxy, Cl, Br; R4 is methyl, ethyl; X is Cl, I, Br), hydrolyzing the reaction product, if necessary, treating the obtained compound of formula III with hydrochloric acid, and subsequently preferentially depositing the crystals of the obtained hydrochloride from the mixture solvent of ethanol with diisopropyl ether.