Experimental and theoretical studies have been made on the nature of concentrated ozone. We proved that ozone with concentrations above 50 vol% can produce a passivated layer on the surface of stainless steel, which is considerably inactive to ozone decomposition. The ozone decomposition rate is strongly dependent on temperature, concentration and pressure. We also determined the activation energy and order of reaction for the decomposition. Moreover, our results reveal that N-2, Ar and He have no effects on ozone decomposition, while CH4 and H-2 act as catalysts and CO reacts with ozone under ordinary temperature and pressure conditions.