Deactivation of ozone catalysts at high humidity and their transient degradation mechanisms are two issues of interest. Herein, we constructed a group of MOFs, denoted as MIL-100(Mn), MIL-100(Er), and MIL-100(Mn0.33Er0.67). The optimal performance was achieved by MIL-100(Mn0.33Er0.67), which maintains 95% removal efficiency for more than 72 h over wide humidity fluctuation (10% RH – 90% RH). Compared to MIL-100 (Er) and MIL-100 (Mn), it has improved by 55% and 46%, respectively. Experimental and theoretical calculations indicate that the adsorption of H2O on the above catalysts is significantly weaker than that of O3. Distinguishing from MIL-100(Mn), the introduction of Er provided additional active sites and expedited the removal of the intermediate (O2–, O22–). Unlike the shedding of an O2 by M-O2 to form M (M-open metal sites), the pathway by which O3 directly attacks M-O2 to form M-O3 is thermodynamically spontaneous, and a new O3 degradation mechanism was proposed.