The fluorination reaction of 1,1,1-trifluoro-2,2,-dichloroethane (CF₃CHCl₂, HCFC-123) to pentafluoroethane (CF₃CHF₂, HFC-125) has been studied under atmospheric prassure at the temperature range of 250-380℃ over Cr-based catalyst. The catalyst comprised Cr, one component selected from the group consisting of Mg or Ca and at least one metal component selected from the group consisting of Ce, Zn and Ni. The effects of catalyst compositions, molar ratio of reactants (HF/HCFC-123), reaction temperature, contact time on the catalytic activities were extensively investigated. The catalytic performance of chromium oxide mixed with metallic compounds has been found to be much improved as compared with that of chromium oxide catalyst alone. Especially, the presence of metallic compounds in the chromium oxide catalyst has shown the outstanding capability of slowing down the catalyst deactivation by retarding the carbon deposition on the catalyst.