(S)-(-)-α-cyano-3-phenoxybenzyl alcohol, which is the alcohol moiety of pyrethroids, effective insecticides, is prepared by reacting organic carboxylic acid ester, such as acetic acid ester, of racemic (R.S)-α-cyano-3-phenoxybenzyl alcohol with an esterase, wherein the ester of (S)-(-)-α-cyano-3-phenoxybenzyl alcohol is predominantly hydrolyzed. Thus. asymmetric hydrolysis permits optical resolution of the (S)-(-)-isomer alcohol from the ester of its antipode, in a high optical purity. The esterase may be of microorganism or animal pancreas or liver.