Hydrogenation is an important method of chemical modification, which improves the physical, chemical, and thermal properties of diene elastomers. It is also a useful method for preparation of polymers with unusual monomer sequences. Natural rubber (NR) could be quantitatively hydrogenated to a strictly alternating ethylene-propylene copolymer using a homogeneous RhCl(PPh3)(3) catalyst. The effect of concentration of rubber, catalyst and triphenyl phosphine, temperature, pressure, and solvent on the course of hydrogenation were evaluated. The thermal properties of the hydrogenated NR are compared with NR.