Pharmaceutical wastewaters are generated through complex manufacturing processes that contain a variety of organic and inorganic constituents, and are usually characterized by a high concentration of chemical oxygen demand (COD), suspended solids, dissolved solids (salts), toxicity, and refractory compounds. In this paper, wet peroxide oxidation (WPO) was adopted to treat pharmaceutical wastewater. Central composite design, an experimental design for response surface methodology (RSM), was used to create a set of 30 experimental runs needed for optimizing operating conditions. The experimental results show that WPO could effectively reduce COD by 97.5% at optimum conditions: temperature is 260ºC, H₂O₂ excess (HE) is 0, the initial concentration of pharmaceutical wastewater is 45,000 mg/L, and reaction time is 10 min. WPO process is possibly suitable for a primary treatment for pharmaceutical wastewater. Response surface methodology (RSM) could be effectively adopted to optimize the operating multifactors in a complex WPO process.