Adhesion between dentin and MMA resin was investigated using initiator systems consisting of barbituric acids/cupric chloride.Without adhesion-promoting monomers, an adhesive strength of 13.9MPa was obtained between dentin treated with 10wt% citric acid-3wt% CuCl₂ solution and MMA resin using a 1, 3, 5-trimethyl-2-thiobarbituric acid/CuCl₂ initiator system, As a model experiment to understand the mechanism of the adhesion, MMA was polymerized in the presence of decalcified dentin sheet treated with various solutions.Curing time, molecular weight of PMMA, and grafting percent of PMMA to dentin sheet were investigated.The findings suggested that cupric ions absorbed onto dentin are involved in promoting the polymerization of MMA and thus affect the bond strength of the MMA resin to dentin.