The hydrolysis of chloropentafluoroethane (CFC-115) is investigated using alumina-zirconia catalysts prepared from boemite and gamma-alumina composed of various different alumina contents. In the case of alumina-zirconia (alumina-zirconia(B)) catalysts prepared from boemite, a catalyst with an alumina content of 90 wt% exhibited the highest rate of hydrolysis. The acidity of these catalysts is found to correlate to the rate of hydrolysis, however, the hydrolysis rate increases linearly with an increase in acidity. On the other hand, in the case of alumina-zirconia (alumina-zirconia(A)) catalysts prepared from gamma-alumina, the hydrolysis rate and acidity increase with an increase in alumina content. The hydrolysis rate increases linearly with an increase in acidity. The hydrolysis rate and acidity over alumina-zirconia(A) are removed from the hydrolysis rate and amount of acidity over alumina-zirconia(B), respectively. The residual hydrolysis rate increases linearly with the residual acidity. Thus, alumina-zirconia(B) catalysts have been determined to bear two types of acidity.