Cryptosporidium parvum oocyst disinfection experiments were performed using ozone at bench-scale in batch reactors. The water matrix was filter effluents collected from a full-scale facility in different seasons but with similar water quality. Cell tissue culture (FDM-MPN) was used to assess the viability of C. parvum oocysts. The disinfection kinetics showed no significant difference in waters from different seasons. The simple Chick–Watson model was found to be the best fit model for MPN data in combination with first-order-plus-demand ozone decay kinetics. The CT value for 99% inactivation was determined to be 19.5 mg-min l−1 at 15°C when pooling data together, which was larger than values reported in other studies.