Catalytic ozonation of p-Chloronitrobenzene (pCNB) in aqueous solution has been carried out where pumice have been used as the catalysts. The presences of the catalysts significantly improve the degradation efficiency of pCNB and the utilization efficiency of ozone. The adsorption of pCNB is too small to make a significant contribution to the degradation of pCNB in either of the processes of catalytic ozonation by pumice. Addition of t-BuOH causes the obvious decrease of degradation efficiency, suggesting that degradation of pCNB follows the mechanism of hydroxyl radical (OH) oxidation. Some of the main operating variables like dosage of catalyst and reaction temperature exert a positive influence on the degradation efficiency of pCNB.