Catalytic oxidation of benzene with ozone was carried out over alumina-supported manganese oxides. Manganese oxides was highly dispersed on alumina at low loading levels (Mn < 2.5 wt%) and aggregated Mn3O4 crystallites were formed at the high loading levels (> 7.5 wt%). Both the Mn oxide species were active for benzene oxidation with ozone, and the former showed slightly higher activities. TPO studies of used catalysts revealed that the oxidation behavior of benzene was not so much influenced by the Mn loadings.