Graft polymerization of MMA with functional monomers onto silk was carried out to investigate the relationship between the grafting and adhesion of the resin to dentin. Functional monomers did not always promote the graft polymerization onto silk. 4-META, one of the functional monomers, increased the degree of grafting without a conformation change of the silk. Phenyl-P decreased the grafting and also changed the conformation of the silk. On the other hand, these monomers promoted the adhesion of resin to dentin. The graft polymerization of monomers onto collagen was not always necessary for the adhesion of resin to dentin. It was important for the adhesion, that monomers inter-penetrated into the dentin well, and were polymerized in situ.