Optically active β-lactams were synthesized by lipase-catalyzed kinetic resolution using the enantioselective hydrolysis of N-acyloxymethyl β-lactams (3) in an organic solvent and the transesterification of N-hydroxymethyl β-lactams (2) with vinyl acetate. A variety of highly optically pure β-lactams (2 and 3) possessing some substituents at the 3, 4, or both positions were obtained and the optically active N-hydroxymethyl β-lactams prepared were converted into useful N-unsubstituted ones without racemization.