With electrochemical impedance spectroscopy (EIS), the ionic resistances of the catalyst layer (CL) were measured at different current densities after the proton exchange membrane (PEM) fuel cell suffered the subfreezing temperature. Compared with those of the CL before being frozen, the ionic resistances unexpectedly decreased a little, which accorded well with the polarization results. Considering that the frequency-dependent penetration depth was small in the high frequency region, a semi-quantitative method based on the finite transmission-line equivalent circuit was followed to investigate the ionic resistance profile across the whole CL. The results indicated that the change of the ionic resistance profile was not uniform across the CL after the cell experienced freeze/thaw cycles, which was more evident at the higher current densities. (c) 2007 Elsevier B.V. All rights reserved.