The reaction of CCl4 with prefluorided Cr2O3 has been studied by temperature-programmed and isothermal methods. Temperature-programmed reaction showed that CCl3F and CCl2F2 were produced simultaneously with activation energies of 64.5 and 62.5 kJ mol(-1), respectively, for the surface exchange reaction. It also allowed evaluation of the surface fluoride radius, a value of 1.86 Angstrom. being obtained which is slightly higher than the literature value of 1.33 Angstrom. Isothermal reaction at 523 and 673 K of CCl4 produced simultaneous and instantaneous sharp peaks of CCl3F and CCl2F2. The fluoride ion radius derived from the 523 K experiment was 2.8 Angstrom, suggesting that integration of the peak was terminated prematurely while the value at 673 K was 2.6 Angstrom, suggesting involvement of the subsurface fluorine ions.