Reducing the loading of noble Pt-based catalyst is vital for the commercialization of proton exchange membrane fuel cell (PEMFC).However,severe mass transfer polarization loss resulting in fuel cell perfor-mance decline will be encountered in ultra-low Pt PEMFC.In this work,mild oxidized multiwalled carbon nanotubes (mMWCNT) were adopted to construct the catalyst layer,and by varying the loading of carbon nanotubes,the catalyst layer structure was optimized.A high peak power density of 1.23 W·cm 2 for the MEA with mMWCNT was obtained at an ultra-low loading of 120 μg·cm-2 Pt/PtRu (both cathode and anode),which was 44.7％ higher than that of MEA without mMWCNT.Better catalyst dispersion,low charge transfer resistance,more porous structure and high hydrophobicity of catalyst layer were ascribed for the reasons of the performance improvement.