This study aims to investigate degradation mechanisms and kinetics of phenoxyacetic acid by ozonation in aqueous solution. The optimized operating condition was achieved by phenoxyacetic acid and total organic carbon (TOC) removal based on the studies of the effects of various parameters, such as pH value (4-12), the initial concentration of phenoxyacetic acid (100-2000 mg L-1) and the ozone dosage (16-48 mg min(-1)). A series of intermediates were formed in the ozonation process and detected by GC/MS and HPLC analysis, such as phenyl formate, salicylic acid, phenol, oxalic acid and small molecule acids. A possible degradation pathway of phenoxyacetic acid was proposed. The kinetic analysis showed that phenoxyacetic acid degradation was in slow kinetic regime based on the results of Ha. This paper can provide basic data and theoretical reference for pharmaceutical wastewater treatment by ozonation. (C) 2015 Elsevier B.V. All rights reserved.