Liquid natural rubber (LNR) is a low-molecular-weight polymer resulting from degradation of natural rubber (NR) with a similar monomer along the backbone chain. Hydrogenated LNR (HLNR) was synthesized from LNR, in which diimide generated through the thermolysis of p-toluenesulfonyl hydrazide (TSH) served as the source of hydrogen. The products' structure was confirmed on the basis of changes in main peaks featuring carbon–carbon unsaturated bonds in Fourier-transform infrared and nuclear magnetic resonance spectra after hydrogenation. Gel-permeation chromatography showed that HLNR had a lower molecular weight (Mw < 104) than LNR (Mw < 105) and NR (Mw > 106) because of chain degradation during hydrogenation. The targeted conversion percentage (>90%) was attained by manipulating the reaction parameters. A ratio of 3:1 TSH/LNR was optimum for achieving a high percentage of hydrogenation at 130 °C in a 6 h reaction period. Thermogravimetric analysis indicated that the hydrogenation process increased the degradation temperature of LNR. HLNR also can act as a compatibilizer to improve the miscibility of natural rubber/polystyrene blends based from an optical microscope.