PURPOSE: To easily obtain an N-substituted aziridine compound having high optical purity on an industrial scale in high yield by subjecting an optically inactive meso-aziridine to asymmetric hydrolysis reaction with an acylase.

CONSTITUTION: The objective chiral aziridine compound of formula II can be produced by the asymmetric hydrolysis of a compound of formula I (R1 is imino-protecting group; R2 is lower alkanoyl) with an acylase which is a hydrolase of amide bond [preferably Amano P (product of Amano Pharmaceutials)]. The compound of formula II is useful for the production of (2S,3S)-2,3-aziridino-4-hydroxybutyric acid methyl ester which is a synthetic raw material for an important intermediate forming a principal skeleton for the synthesis of FR900482 substance and FK973 substance.