The decomposition of monocrotophos (cis-3-((dimethoxyphosphinyl)oxy)-N-methylcrotonamide) in aqueous solution by ozonation was studied under various solution pH values, gaseous ozone dosages, and alkalinity levels. The decomposition rate of monocrotophos was increased with decreasing solution pH and increasing ozone dosage. The presence of alkalinity (HCO3- and CO32- species) inhibited the decomposition of monocrotophos to certain extents, but severely retarded the mineralization of the organic intermediates. The presence of Fe2+ and Mn2+ ions interfered with the decomposition of monocrotophos in acidic solutions. The decomposition pathway of monocrotophos was proposed and the breakage of the carbon-carbon double bond by ozonation was found to occur at first to form various nitrogen-and phosphorus-containing compounds, and subsequently decomposed to be H2O, CO2, NO3-, and PO43- species. The quasiglobal kinetics based on a simplified consecutive-parallel reaction scheme was developed to describe the temporal behavior of monocrotophos decomposition in an aqueous solution by ozonation.