RuHCl(CO)(PCy3)(2) (1) dissolved in 1-butyl-3-methylimidazolium tetrafluoroborate (2) molten salt is able to reduce selectively NBR to HNBR under hydrogen partial pressures between 10 and 40 bar at 100-160 degrees C in a typical two-phase catalytic reaction. Reaction rates between 0.059 (mmol Ru)(-1).min(-1) and 1.65 (mmol Ru)(-1.)min(-1) were obtained depending on the reaction parameters and increasing with the volume of the molten salt. The overall process has an apparent activation energy of 47 +/- 3 kJ.mol(-1). The recovered ionic catalyst solution can be reused several times without significant changes in the catalytic performance (selectivity and activity).