The kinetics of cationic photoinitiated polymerization of di-epoxy monomers: 3, 4-epoxycyclohexylmethyl-3′, 4′-epoxycyclohexane carboxylate have been investigated by using differential scanning calorimetry (DSC). The DSC observed heat flow was divided into two kinds of heat flow, one from the polymerization and the other from UV-light energy. Upon 1J/cm² of UV-irradiation, the percent conversion of monomer is only 40% when all the polymer active cations have terminated. A bimolecular chain termination process will be taken to account for the remainder of polymer active cation immediately after UV-lamp off. It is estimated that two chain transfer reactions occur almost simultaneously and they appear one bimolecular terminatiom reaction. Afterwards the polymer active cations terminate with photoinitiator species mainly.