Catalytic hydrothermal oxidation of p-chlorophenol has been examined using two types of reactor systems, i.e., a flow-type reactor system in which the catalyst powder was suspended in the reaction mixtures and a fixed-bed reactor system in which the sintered catalyst was packed in the reactor. Cu- or Fe-grafted TiO2 was employed as a catalyst and hydrogen peroxide was used as an oxidizing reagent. The decomposition efficiency of p-chlorophenol treated by the flow-type reactor system is considerably enhanced with the help of Cu-grafted TiO2 at reaction temperatures around 200 degrees C; whereas, little effect is observed at any temperature for Fe-grafted TiO2. It is suggested that the Fenton-type reaction catalyzed by Cu ions contained in the Cu-grafted TiO2 and/or dissolved out in the solution undergoes substantial acceleration at high temperatures, leading to the increased generation of OH center dot radicals that can effectively oxidize p-chlorophenol. On the other hand, it appears that the Fe-ion-catalyzed Fenton reaction is suppressed in the hydrothermal environment. The prolonged treatment of p-chlorophenol using the fixed-bed reactor system, that is more suitable for practical use than the flow-type one, has also been performed with Cu-grafted TiO2 catalyst at a reaction temperature of 200 degrees C. The result demonstrates that it is possible to treat p-chlorophenol continuously for up to 36 h without significant loss of the catalytic activity.