The water transport behavior of the cathode catalyst layer (CCL) in a proton exchange membrane fuel cell (PEMFC) was investigated by comparing the performance of several cells containing different microporous layers (MPLs). The capillary pressure and effective diffusivity of the cathode gas diffusion layer (GDL) and the CCL play an important role in the transport of water generated in the PEMFC. Experimental data for various inlet humidities and air stoichiometries were evaluated using the modified water vapor activity with the capillary pressure of the MPL. The capillary pressures in the MPLs and CCL are approximated using a polynomial function of liquid saturation. There was a significant increase in the diffusion resistance of oxygen in the CCL, while that in the MPLs and CCL was moderate, which indicates that the CCL is susceptible to flooding.