A nonisothermal, two-phase model was developed to investigate simultaneous heat and mass transfer in the cathode gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC). The model was applied in two-dimensions with the in-plane (i.e., channel-to-land) and through-plane (i.e., catalyst layer-to-channel) directions to investigate the effects of anisotropy of GDL. For the first time, the anisotropy in the GDL properties was taken into account and found to be an important factor controlling the temperature distribution in the GDL. The maximum temperature difference in the GDL was found to be a strong function of GDL anisotropy. A temperature difference of up to 5 degrees C at a cell voltage of 0.4 V was predicted for an isotropic GDL while it reduced to 3 degrees C for an anisotropic GDL. Significant effect of temperature distribution on liquid water transport and distribution was also observed. In addition, the latent heat effects due to condensation/evaporation of water on the temperature and water distributions were analyzed and found to strongly affect the two-phase transport. (c) 2007 The Electrochemical Society.