To accomplish the goals of cost reduction and durability improvement of polymer electrolyte water electrolysis (PEMWE), we report a titanium oxide and molybdenum oxide composite (TiO2-MoOx) as a support for the iridium (Ir) nanoparticle catalyst (Ir/TiO2-MoOx) toward oxygen evolution reaction (OER). Incorporation of Mo(V) and Mo(VI) into TiO2 significantly enhances the electrical conductivity of TiO2. During the synthesis of Ir nanoparticles on TiO2-MoOx, Mo(V) is oxidized to Mo(IV) with suppressing oxidation of Ir(III) to Ir(IV). Consequently, Ir/TiO2-MoOx forms higher fraction of the OER-active Ir(III) species on Ir surface enhancing OER activity of Ir catalyst. During OER, the chemical interaction between Mo and Ir keeps in Ir(III) and lessens the dissolution of Ir(III), improving the durability of Ir/TiO2-MoOx. Thus, Ir/TiO2-MoOx exhibits superior OER activity and durability. The single cell test results demonstrate that, as an anode catalyst, Ir/TiO2-MoOx can improve the performance and durability of the PEMWE cell than Ir black.