Syntheses and radical copolymerization behavior of N-methacryloyl-L-leucine methyl ester (MA-(L)-L-M) and its optical isomer (MA-(D)-L-M) have been examined. From their melting points and crystal X-ray analysis, MA-(L)-L-M and MA-(D)-L-M might be suggested to form a racemic compound associated at the amide moiety by a hydrogen bond. Radical copolymerizations of MA-(L)-L-M and MA-(D)-L-M were carried out using AIBN as an initiator (1 mol %) in chlorobenzene (1 M) to afford the corresponding copolymers as n-hexane-insoluble pacts with <(M)over bar (n)>, 77 000-120 000. The conversions of the monomers were almost quantitative in any case. The T-g of the copolymer having an equimolar ratio of L- and D-units was lower than those of the corresponding homopolymers. while the solubility of the copolymer in ether was higher than those of the homopolymers. The total rate of radical copolymerization of MA-(L)-L-M and MA-(D)-L-M was smaller than those of the homopolymerizations of the both monomers.