Nowadays, highly efficient decomposition of ozone is still technologically challenging, especially in the presence of high humidity levels. In this study, Cu2O/reduced graphene oxide composite (Cu2O/rGO) is in-situ synthesized by reducing a mixed solution of Cu2+ and GO. This developed catalytic system exhibits 100% ozone (20 ppm O-3/air) decomposition efficiency at room temperature with high stability. Importantly, the ozone conversion could be still above 96% at high relative humidity levels (ca. 90%) after 10 h of continuous operation. The excellent performance is suggested to be attributed to the highly active ultrafine Cu2O nanoparticles heterogeneously nucleated on rGO, which facilitate necessary electron density by the transfer of it between Cu2O and rGO phases.