An environmentally friendly method to decontaminate the olive mill wastewater, which is encountered as a major environmental problem is presented in this study. The removal of both polyphenolic and aromatic content and the degradation of wastewater of olive mill supplied from Mersin/Turkey region were investigated by the subcritical water oxidation method using H2O2. The central composite design of response surface methodology was used to assess the effects of temperature, treatment time, and the concentration of oxidising agent. The reliability of the employed method was proved by ANOVA. The optimum experimental parameters were determined and theoretical equations were proposed in each case. The highest chemical oxygen demand removal, dephenolisation and dearomatisation values were obtained as 85.74, 96.13 and 95.94 %, respectively.