Mesoporous transition metal oxide catalysts are well-used in the elimination of volatile organic compounds. In this study, we developed an efficient method for the preparation of mesoporous-Mn 3 O 4 (m-Mn 3 O 4 ) without the use of templates or surfactants. In this method, KCl protects oxygen defects on the surface of fresh Mn 3 O 4 crystallites. m-Mn 3 O 4 shows higher ameliorative catalytic activity than bulk-Mn 3 O 4 (b-Mn 3 O 4 ) and calcined-Mn 3 O 4 (c-Mn 3 O 4 ), achieving toluene catalytic oxidation of T 10 and T 90 (the temperature at a conversion rate of about 10% and 90%) at 191 ℃ and 230 ℃, respectively (WHSV = 40,000 ml·g −1 ·h −1 ). Based on various characterizations, the prepared m-Mn 3 O 4 has large specific surface area and abundant oxygen defects, and thus can provide more surface active sites, which give it superior toluene combustion activity.