Effect of partial metal reduction on the catalytic property of cobalt has been studied for Co/Al₂O₃ catalyst reduced to different extents. The sample catalysts have been tested for CO and H₂ adsorption, CO hydrogenation, and Temperature Programmed Surface Reaction(TPSR). Major effect of the incomplete metal reduction on the surface property of cobalt is that hydrogen adsorption is significantly suppressed. This behavior is responsible to enhanced olefin production and retarded CO dissociation as observed for the catalysts of lower metal reduction. Changes in the kinetic parameters of CO hydrogenation on partially reduced cobalt may be explained from its gas adsorption behavior.