The partial hydrogenation of benzene to cyclohexene based on thermodynamics, kinetics and mechanism of the reaction have been discussed. Ruthenium catalysts are effective and have been widely used for obtaining high yields of cyclohexene, the effects of organic and inorganic modifiers as well as mass transfer limitations on the selectivity to cyclohexene are illustrated. The behavior of the ruthenium catalyst prepared with sol-gel method in this reaction is also given. Finally, a depiction of the interaction of ruthenium and zinc on the performance of using the ruthenium catalyst to obtain high yields of cyclohexene is reported.