Abstract: The present invention relates to a process in which N-acyl form of DL-erythro 3-substituted serines represented by the following general formula (1): (wherein, R1 means an alkanoyl group having 1-10 carbons, a benzoyl group, a halogen-substituted alkanoyl group having 1-5 carbons or a halogen-substituted benzoyl group, and R2 means a phenyl group or a cyclohexyl group) is subjected to asymmetrical hydrolysis with L-aminoacylaseorD-aminoacylase, there by giving unreacted N-acyl-D-erythro3-substituted serine in the case of L-aminoacylase or hydrolyzed D-erythro 3-substituted serine in the case of D-aminoacylase. The D-erythro forms are useful as an intermediate for medicines, for example, known to be useful as an anti-HIV drug (WO 01/40227).