Metathesis hydrogenation of deproteinized natural rubber (NR) latex was studied using 2nd generation Grubbs catalyst. More than 97% hydrogenation was achieved under mild conditions and without organic solvent addition other than that used to dissolve the catalyst. The olefin conversion plot exhibited an S-curve characteristic which indicated the effect of competition between the metathesis reaction and the hydrogenation reaction. Molecular weight of NR dramatically changed along the reaction time in the first region due to the metathesis reaction and then slightly changed in the second region where the hydrogenation consumption plot obeyed a first-order kinetic model. The kinetic behavior of the hydrogenation region increased with an increase in catalyst concentration and hydrogen pressure. The results showed an inverse behavior with an increase in rubber concentration. The apparent activation energy over the temperature range of 80-96 degrees C for the hydrogenation of metathesized natural rubber was found to be approximately 169 kJ/mol. (C) 2011 Published by Elsevier B.V.