PURPOSE: To produce the optically active amino acid derivative by treating an N-substituted oxycarbonyl-D,L-amino acid with a microorganism capable of stereoselectively decomposing the compound.

CONSTITUTION: An N-substituted oxycarbonyl-D,L-amino acid of the formula (R1 is the a-substituent of an amino acid; R2 is alkyl, aralkyl, alkenyl) and/or its salt (e.g. N-allyloxycarbonyl-D,L-aspartic acid β-ethyl ester) is treated with the cells, cultured product or treated product of a microorganism (e.g. Cellulomonas.flavigena ATCC 482) belonging to the genus Cellulomonas, Zoogloea, Rhodotorula, Rhodosporidium, or Kloeckera and capable of stereoselectively hydrolyzing the N-substituted oxycarbonyl-D,L-amino acid, followed by subjecting the treated product to an optical resolution to provide the L-amino acid and the D-N-substituted oxycarbonyl amino acid derivative.