The electrode of polymer electrolyte fuel cell (PEFC) consists of the porous catalyst layer and gas diffusion layer (GDL). Quantitative evaluation of the influence of these porous layers' degradation on the cell performance was attempted. The cell was assembled by using the catalyst layer or GDL, which had been corroded ex situ, as the cathode and the cell performance was characterized. The oxygen diffusion polarizations of the catalyst layer and that of the GDL were evaluated from the polarization curves. The polarization curves before and after a long-term operation were also analyzed by the same way, and the influences of the degradation of catalyst layer and GDL were evaluated. The increase of the gaseous diffusion loss in the catalyst layer was found to cause the cell performance loss mainly from the analysis of the simulated corrosion test and the long-term operation cell. (C) 2009 Elsevier B.V. All rights reserved.