Highly dispersed MnO2 nanoparticles were supported on ZSM-5 zeolite and used for ozone-catalytic oxidation (OZCO) of gaseous benzene. The prepared MnO2/ZSM-5 is very active in complete oxidation of benzene even at ambient temperature. Benzene conversion and CO2 selectivity reached 100% and 84.7%, respectively, while no CO byproduct was formed. However, while it ran well in air with low humidity, the catalyst got slowly deactivated after a long run in humid air. The possible reasons responsible for its deactivation were investigated. The structural changes of catalysts and the intermediates generated from benzene oxidation should not be the key cause for catalytic deactivation. Benzene OZCO is highly sensitive to water vapor and water poisoning mainly accounted for the deactivation of MnO2/ZSM-5 due to its occupying of catalytic active sites and adsorption centers. The improved catalytic activity and suppression of deactivation can be easily achieved by reducing water vapor or slightly increasing reaction temperature. (C) 2014 Elsevier B.V. All rights reserved.