The graft copolymerization of MMA onto human dentin was studied with the redox system usingK2S2O8+NaHSO3 as initiator. The IR spectrum of the copolymer showed the presence of C=Oband at 1720 cm-1,C--O at 1260-1, CH3, at 2850 cm-1. indicating the presence of polymerized me-thacrylate on the detin. The ppt. of the acid hydrolysis of the graft copolymer showed an -NH3+band of amino acid at 3200 cm-1. Most marked percent decreases in contents of amino acids inthe acid hydrolysate were observed in serine,tyrosine and methionine.The absolute amounts of glycine,alanine and proline have also decreased markedly.This suggests that it was most probable that the graft copolymerization occurred at these residues.The tubular stripes and cross section cavities of dentin tublets were covered with a high polymer graft which could be seen from the SEM pictures.The mol.wt.of this grafted high polymer,as determined by GPC:was higher than that of the homopolymer and the former had a broader mol.wt distribution.All these facts suggested that a genuine graft copolymerization of MMA onto human dentin occurred.