Process for preparing 2,3,3,3-tetrafluoropropene, comprising the following steps: (a) catalytic reaction of 1,1,1,2,3-pentachloropropane and/or 1,1,2,2,3-pentachloropropane with HF into product 2-chloro-3,3,3-trifluoropropene; (b) catalytic reaction of the thus-obtained 2-chloro-3,3,3-trifluoropropene into 2,3,3,3-tetrafluoropropene, wherein step (b) comprises: (i) contacting 2-chloro-3,3,3-trifluoro-1-propene with hydrogen fluoride HF in gas phase in the presence of a fluorination catalyst and an oxygen or chlorine co-feed under conditions sufficient to produce a reaction mixture; (iia) separating the reaction mixture of step (i) into a first stream comprising HCl, 2,2,2,3-tetrafluoropropene and a second stream comprising HF, unreacted 2-chloro-3,3,3-trifluoro-1-propene and 1,1,1,2,2-pentafluoropropane; Or (iib) separating the reaction mixture of step (i) into HCl and a stream containing the fluorinated products; (iib') separating said stream (iib) containing the fluorinated products into a first stream comprising 2,2,2,3-tetrafluoropropene and a second stream comprising HF, unreacted 2-chloro-3,3,3-trifluoro-1-propene and 1,1,1,2,2-pentafluoropropane; (iii) recycling at least a part of the second stream at least in part back to step (i). (a) catalytic reaction of 1,1,1,2,3-pentachloropropane and/or 1,1,2,2,3-pentachloropropane with HF into product 2-chloro-3,3,3-trifluoropropene; (b) catalytic reaction of the thus-obtained 2-chloro-3,3,3-trifluoropropene into 2,3,3,3-tetrafluoropropene, wherein step (b) comprises: (i) contacting 2-chloro-3,3,3-trifluoro-1-propene with hydrogen fluoride HF in gas phase in the presence of a fluorination catalyst and an oxygen or chlorine co-feed under conditions sufficient to produce a reaction mixture; (iia) separating the reaction mixture of step (i) into a first stream comprising HCl, 2,2,2,3-tetrafluoropropene and a second stream comprising HF, unreacted 2-chloro-3,3,3-trifluoro-1-propene and 1,1,1,2,2-pentafluoropropane; Or (iib) separating the reaction mixture of step (i) into HCl and a stream containing the fluorinated products; (iib') separating said stream (iib) containing the fluorinated products into a first stream comprising 2,2,2,3-tetrafluoropropene and a second stream comprising HF, unreacted 2-chloro-3,3,3-trifluoro-1-propene and 1,1,1,2,2-pentafluoropropane; (iii) recycling at least a part of the second stream at least in part back to step (i). (i) contacting 2-chloro-3,3,3-trifluoro-1-propene with hydrogen fluoride HF in gas phase in the presence of a fluorination catalyst and an oxygen or chlorine co-feed under conditions sufficient to produce a reaction mixture; (iia) separating the reaction mixture of step (i) into a first stream comprising HCl, 2,2,2,3-tetrafluoropropene and a second stream comprising HF, unreacted 2-chloro-3,3,3-trifluoro-1-propene and 1,1,1,2,2-pentafluoropropane; Or (iib) separating the reaction mixture of step (i) into HCl and a stream containing the fluorinated products; (iib') separating said stream (iib) containing the fluorinated products into a first stream comprising 2,2,2,3-tetrafluoropropene and a second stream comprising HF, unreacted 2-chloro-3,3,3-trifluoro-1-propene and 1,1,1,2,2-pentafluoropropane; (iii) recycling at least a part of the second stream at least in part back to step (i).