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Hydrogenated nitrile butadiene rubber (HNBR) is a high?performance elastomer widely used in the petrochemical and automotive industry. A Ruthenium?based catalyst [1,3?Bis(2,4,6?trimethylphenyl)?2?imidazolidinylidene]?[2?[[(4?methylphenyl) imino]methyl]?4?nitrophenoyl]chloro?[3?phenyl?indenylidene]ruthenium(II) (M41) was investigated for the direct hydrogenation of NBR latex. The catalytic selectivity for the hydrogenation of ?C=C? bond instead of ?C?N group was confirmed by both FT?IR and 1H NMR. The effects of reaction conditions (such as temperature, pressure, catalyst levels, agitation speed and solid content) on the hydrogenation reaction were examined, and the hydrogenation products with over 95 mol% conversion were obtained for only 3 h with a catalyst/NBR ratio of 0.05 wt% and no gel was formed within HNBR. The results suggest that the current limitations in the hydrogenation of NBR latex could be addressed with this catalyst.This article is protected by copyright. All rights reserved.