This invention concerns a process for reducing a refining catalyst before it is put into use, the catalyst containing a support and an active phase based on at least one noble or non-noble metal of group VIII or of group Ib of the periodic classification of elements, consisting of:(a) impregnating the catalyst with an aqueous or organic solution of a reducing agent,(b) decomposing the reducing agent by heating with a catalyst, and(c) drying the catalyst thus obtained.The catalyst is used in selective hydrogention of a feed such as olefin, acetylenes, diolefins etc.