Oxidation of some toxic organic compounds in supercritical water is investigated in the presence of a solid catalyst in an isothermal plug flow fixed-bed reactor. Comparison between catalyzed and noncatalyzed oxidations indicates that the conversions are much higher when the catalyst is present. It is also found that the heterogeneous oxidation route forms less intermediate products during the decomposition of organics such as benzoic acid and 1-methyl-2-pyrrolidone in carbon dioxide.