The treatment is an economic tool to meet the diversity of industrial activities in developing country like Egypt. The present study introduces serious trials to partially remove organic matter in industrial wastewater and their using advanced oxidation process (AOP). Sampling program was carried out according to standard international methods for treating industrial wastewater in terms of wastewater quality parameters such as Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD) to meet the optimum conditions using advanced oxidation process (AOP).  The study aims to apply advanced oxidation process, through Fenton reaction, in secondary treatment of both mixed and industrial wastewater. The research focused on studying the optimum dose of hydrogen peroxide, initial reaction pH value and the retention time to treat influent fresh industrial and mixed wastewater samples. The study samples were fresh industrial and mixed wastewater samples collected from the influent of three different industries. The chosen samples were, namely, Dairy Products Industry, Olive Oil Industry and Mixed Wastewater located in industrial area in El-Obour City, Qalioubeya, Egypt. The study experiments were carried out at the laboratories of National Research Center (NRC) according to the. The results showed that the overall optimum dose of H2O2 to treat dairy products is 25 ml /l at contact time of 10 minutes and initial reaction pH value of (4). Whereas, the overall optimum dose of H2O2 to treat olive oil industry is 10 ml /l at contact time of 20 minutes and initial reaction pH value of (4). Also, the
overall optimum dose of H2O2 to treat mixed industrial- domestic wastewater is 10 ml/l at contact time of 10 minutes and initial reaction pH value of (4)