Catalytic and non-catalytic supercritical water oxidation of p-nitrophenol contained in wastewater was performed using compressed air and hydrogen peroxide as an oxidant, respectively. In catalytic process, the supported Mn2O3/Ti-Al oxide composite catalyst was employed to accelerate the reaction rate. Experiments were conducted to investigate the effect of temperature, pressure, oxygen excess or dosage of hydrogen peroxide and residence time on the destruction of p-nitrophenol. Appropriate reaction conditions were obtained for both processes. Based on the products generated in reaction, possible reaction pathways were speculated. A possible mechanism was also proposed for the catalytic process according to the experiments focused on the crystal structure transformation in catalyst MnO2. The comparison of the two processes indicated that hydrogen peroxide is a better oxidant without its cost taken into consideration, and the reaction rate of catalytic process is much higher than that in non-catalytic process in spite of the better oxidant used in it. (C) 2015 Elsevier B.V. All rights reserved.