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. Therefore, it must be treated. The treatment of a pharmaceutical wastewater (PWW) using the supercritical water oxidation (SCWO) method was investigated to improve the degradation of the complex-mixture of organic compounds present in the wastewater. The effects of H₂O₂ dosage, reaction time, temperature, initial COD, and concentration of ethylene glycol on COD removal were studied with laboratory bench-scale experiments. The results indicated that the removal process was more effective under experimental conditions. Adding ethylene glycol accelerates the destruction of pharmaceutical wastewater. The best COD removal of pharmaceutical wastewater reached 97.8%. This investigation will provide a fundamental method for developing a pretreatment method of industrial pharmaceutical wastewater with flexibility, simplicity and high activity.