MnO nanoparticles supported on coal-based activated carbon (AC) were facilely fabricated via incipient wetness impregnation method by calcination of manganese acetate in nitrogen. The as-prepared catalysts were characterized by N-2 adsorption-desorption, XRD, TEM, and XPS. It is demonstrated that calcination under inert atmosphere can facilely obtain well dispersed MnO nanoparticles on AC, and the particle size, as well as the surface oxygen species of the catalysts strongly depended on the calcination temperature. The AC supported MnO nanoparticles all exhibited high catalytic activity toward ozone decomposition at room temperature, and an optimal one was displayed as the calcination temperature of 700 degrees C. The smallest particle size of MnO nanoparticles and the most amount of surface oxygen vacancies, were mainly responsible for the highest activity of MnO/AC-700. Moreover, lower loading of Mn was found to be more favorable for stable catalytic performance. This work reported a series of MnO based catalysts for efficient removal of ozone at room temperature for the first time, and may shed new lights on the design of manganese oxides with lower oxidation state for efficient ozone decomposition.