The purpose of this research is to modify natural rubber (NR). The optimum conditions for synthesis of epoxidized natural rubber (ENR) was investigated. The synthesized ENR was modified by hydrogenation reaction. This modified ENR was called HENR. The optimum amount of CuSO4 ·5H2O used in this reaction was investigated. It was found that the optimum condition for synthesizing ENR is as followed. The type of surfactant is POE(12)tridecyl ether and the amount of this surfactant is 5 phr. The highest epoxide content which received from fresh NR latex and concentrated NR latex in selected condition are 25.53 and 22.51% respectively. The highest percentage of hydrogenation from this condition is 67.90%. It can be concluded that after hydrogenation reaction HENR shows higher thermal resistance than that of synthesized ENR.