Method of producing optically active .beta.-lactam derivatives

A method of producing an optically active .beta.-lactam derivative of the general formula ##STR26## wherein A and B are the same or different and each is N, CH or C--R.sup.2 in which R.sup.2 is a lower alkyl group, a phenoxy group, a phenoxy group having 1 to 3 lower alkoxy groups as the substituent or a protected hydroxy group, and R.sup.1 is a hydrogen atom, a lower alkyl group, a phenyl group, a phenyl group having 1 to 3 lower alkoxy groups as the substituent, a benzyl group or a benzyl group substituted with 1 to 3 lower alkoxy groups on the benzene ring, which comprises irradiating with light, in solid phase, an inclusion complex of a nitrogen-containing compound of the general formula ##STR27## wherein A, B and R.sup.1 are as defined above with an optically active host compound.