Metal catalysts such as Fe, Co, Mn, and Pd supported on the activated carbon (AC) were prepared to improve functional groups for the chemical adsorption and catalytic ozonation. Following ascending orders of the phenol decomposition rate, dissolved ozone decomposition ratio and TOC (total organic carbon) removal from experimental results of advanced oxidation process (AOP) were observed: Fe-AC < AC < Co-AC < Mn-AC < Pd-AC. BET analysis results showed that the physical properties of the metal impregnated activated carbon had no effect on the catalytic ozonation, and the catalytic effect was dependent on the kind of impregnated metal. The ratio of the formed concentration of OH radical to that of ozone (RCT) was measured by using the decomposition outcome of p-chlorobenzoic acid, a probe compound that reacts rapidly with OH radical but slowly with ozone. The measured values of RCT were 5.48 × 10-9 and 1.47 × 10-8 for the ozone alone and activated carbon processes, respectively, and 2.13 × 10-9, 1.51 × 10-8, 4.77 × 10-8, and 5.58 × 10-8 for Fe-AC, Co-AC, Mn-AC, and Pd-AC processes, respectively.