The hydrogenation of styrene was studied over two series of nickel/sepiolite catalysts. In order to relate the catalytic behaviour with the active sites present, the nickel component was characterised by a combination of degree of reduction (a), photoelectron spectroscopy (XPS) and infrared spectroscopy of adsorbed carbon monoxide, paying particular attention to the presence and distribution of unreduced nickel and to the metal particle morphology. Catalysts which exhibited the lowest activity per exposed nickel atom in benzene hydrogenation proved to be the most active in styrene hydrogenation, and were the catalysts which showed a high level of unreduced surface nickel. Styrene is proposed to adsorb ’via’ the ethylene double bond at incompletely reduced nickel sites, and is not adsorbed with the ring planar to the surface as is a prerequisite for benzene hydrogenation.