The effect of the sequential application of ozone followed by monochloramine on enteric viruses was investigated using MS2 phage as a surrogate. All experiments were performed in 0.01 M phosphate buffer solution at pH 7.0±0.1. The inactivation of MS2 phage exposed to monochloramine alone at a concentration of about 21 mg/L as Cl2 was found to follow first-order Chick-Watson kinetics with rate constant k = 2.24*10-3 L*mg-1min-1. The inactivation of phage that had first been pretreated with ozone and then exposed to 14 mg/L as Cl2 monochloramine had a rate constant of 3.91*10-3 L*mg -1min-1, about 1.7 times faster than the non-pretreated ones. However, significant tailing occurred in the sequential experiment, probably as a result of the presence of viral aggregates. The precise reason for the tailing has not been fully investigated. Additional research is needed to more fully characterize the observed synergistic effect.