Hydrogenation of liquid natural rubber (LNR) has been successfully accomplished via diimide reduction using hydrazine hydrate/hydrogen peroxide (HH/H2O2 ) system. Each parameter in the system was optimized to obtain maximum hydrogenation degree such as the mass of boric acid, mole ratio of HH: H2O2 , reaction time and reaction temperature. As a result, the highest degree of hydrogenation was achieved at 91.2% using a molar ratio HH: H2O2 of 2:3, in the presence of boric acid as a promoter at 60 °C for 8 hours. In this research, we report on possible side reactions that led to lowering the hydrogenated rubber product. Reactivity of diimide species as well as decomposition of hydrogen peroxide were postulated based on literature reviews to be one of the factors hindering hydrogenation of LNR. The presence of side reactions such as degradation, cyclization, and crosslinking had been confirmed by gel permeation chromatography (GPC), 1H nuclear magnetic resonance (1H NMR), and swelling test, respectively.