Activated carbon was employed as a novel catalyst for supercritical water oxidation of phenol. High-concentrations of phenol were treated in supercritical water at 673 K and 25 MPa with an equivalent amount of oxygen in a reactor packed with activated carbon. Although activated carbon itself was oxidized in the reaction field, its weight decrease was sufficiently slow for its catalytic effect on phenol oxidation to be observed. The catalytic effect of activated carbon consisted of an enhancement of the reaction rate, a decrease in the tarry product yield, and an increase in the gas yield. Under the condition used in this study, 65% of oxygen delivered into the reactor was effectively used for phenol oxidation while only 39% of oxygen was used when no catalyst was applied. This report is the first to indicate the catalytic effect of carbonaceous materials on supercritical water oxidation, and it demonstrates that supercritical water oxidation using lower operation temperatures and inexpensive carbon catalysts may be possible. (C) 2002 Elsevier Science B.V. All rights reserved.