Abstract: The kinetics and mechanism of ozonation degradation of p-nitrochlorobenzene（pCNB）were investigated.The reaction rate constant of pCNB with O₃ was 1.6 L·mol^-1·s^-1 by direct determination.With nitrobenzene and chlorobenzene as the reference compounds, the reaction rate constant of pCNB with ·OH that was determined by means of competition kinetics was 2.6×109 L·mol^-1·s^-1.During the pCNB ozonation degradation, organic nitrogen and organic chlorine were almost completely converted to nitrate and chloride.Ozonation could not reduce TOC obviously.The results of LC-MS and GC-MS showed that the main intermediate products were aromatic substances such as p-chlorophenol, p-nitrophenol, 2-chloro-5-nitrophenol, etc., and non-aromatic substances such as oxalic acid, malonic acid, maleic acid, muconic acid etc.Finally, a possible reaction pathway of ozonation degradation of pCNB was proposed according to these intermediate products.