Chemical oxidation of hazardous liquid waste derived from a pesticide-formulating industry was studied by applying ozone alone and together with coagulation process. Chemical oxidation has been applied to many different fields in wastewater treatment. Pesticide pollution of environmental waters is a pervasive problem with widespread ecological consequences. In the study, ozone was applied both before and after coagulation process to evaluate the most effective treatment combination for the selected industry effluent. Conventional parameters such as pH, TSS (total suspended solids), oil and grease, COD (chemical oxygen demand), and soluble COD were analysed to monitor the efficiencies of each experimental step. Coagulation experiments were conducted by using FeCl 3 and Al 2(SO 4)J-HH 2O as the coagulant dosages varied between 500-3000 mg/1. Ozone gas was supplied with the dosage of 477 mg/min and 5 1/min ozone gas flux rate. Series of experimental investigations showed that COD was reduced approximately 60% after ozonation alone while it decreased about 90% after ozonation following coagulation with ferric chloride. However, the results obtained by the ozonation and chemical treatment with alum were less effective with removal efficiency of about 70%. The complete process of ozonation and coagulation was effective to reduce the pollution potential of the liquid hazardous waste for further treatment facilities.