Selective hydrogenation of benzene to cyclohexene has been studied in rt high pressure slurry reactor using supported ruthenium catalysts. The organic base monoethanolamine (MEA) was found to give better selectivities than the conventional inorganic salt additive (zinc sulphate). Parameters studied were the effects of various supports such as alumina, silica, titania, zirconia, niobium oxide,, etc., benzene to water ratio, catalyst weight, and presence of cyclohexane in the feed. Reusability of the catalyst was also studied.