The nano-Ru/[Bmim][BF4] catalyst was prepared for benzene selective hydrogenation in 1-n-butyl-3- methylimidazolium tetrafluoroborate [Bmim][BF4] by chemical reduction method. TEM analysis of these nanoparticles sho wed the monodisperse Ru0 particles which were prepared by positive dropping method dispersed in the ionic liquids with diameters less than 5nm. The Ru0 particles which were prepared by reverse dropping method agglomerated with diameters more than 10nm. KBH4 was the suitable reductant. The optimum loading of Ru was 1.5%. The hydrogenation activity of Ru/ [Bmim] [BF4] was high and the selectivity of cyclohexene was very low. Selectivity of cyclohexene was only 14.5% at 27.3 % benzene conversion.