An optically active or racemic .alpha.-hydroxyaldehyde represented by the general formula (2), ##STR1## wherein R.sub.1 represents a C.sub.6 -C.sub.14 aryl group, C.sub.1 -C.sub.10 alkyl group, C.sub.3 -C.sub.10 alkenyl group, C.sub.2 -C.sub.10 alkynyl group, C.sub.7 -C.sub.14 aralkyl group, or a group containing a functional group in the organic portion of said groups and R.sub.2 represents a C.sub.1 -C.sub.10 alkyl group, C.sub.2 -C.sub.10 alkenyl group, C.sub.2 -C.sub.10 alkynyl group, C.sub.7 -C.sub.14 aralkyl group, C.sub.6 -C.sub.14 aryl group, or a group containing a functional group in the organic portion of these groups, which is an important intermediate for preparation of pharmaceuticals and agricultural chemicals, and prepared by allowing an optically active or racemic compound represented by the general formula (1), ##STR2## (wherein A represents a C.sub.6 -C.sub.14 aryl group or a C.sub.1 -C.sub.4 alkyl or alkoxy group- or halogen-substituted C.sub.6 -C.sub.14 aryl group and R.sub.1 is as defined above) to react with a Grignard reagent, and thereafter hydrolyzing the reaction product.