The present invention relates to a process for producing pentafluoroethane. More particularly, the subject of the invention is a continuous process for producing pentafluoroethane comprising (i) a step of fluorinating perchloroethylene (PER) with hydrofluoric acid, in the gas phase, in the presence of a catalyst, (ii) a step of separating the products issuing from step (i) in order to give a fraction of light products and a fraction of heavy products, comprising hydrofluoric acid, unreacted perchloroethylene and under-fluorinated products, and (iii) a step of pretreating the fraction of heavy products before recycling to step (i).