To produce pentafluoroethane (CHF2-CF3, HFC-125) which is harmless to the ozone layer, in high purity and good yield by carrying out vapor phase disproportionation of chlorotetrafluoroethane in the presence of a catalyst of a mixture of an oxide of at least one alkaline earth metal selected from Mg, Ca, Sr and Ba, with a trivalent chromium oxide (Cr2O3).

The disproportionation reaction of chlorotetrafluoroethane is carried out at 150-250°C under 1-10 bar pressure while regulating the contact time with the catalyst so as to be 5-30 sec, for example, by passing gaseous chlorotetrafluoroethane (HCFC-124) diluted with an inert gas such as nitrogen through a fluidized bed of the catalyst supported by a carrier such as aluminum fluoride. Preferably, the g-atomic ratio of the chromium to the alkaline earth metal is regulated within the range of (50:1)-(3:1), and the total amount of the chromium and the alkaline earth metal included in the supported catalyst is 5-15 wt.%.