We derive a simple compact expression for impedance of the cathode side of a PEM fuel cell working at a low current density. The solution includes the faradaic impedance, the impedances due to proton and oxygen transport in the cathode catalyst layer (CCL), and due to oxygen transport in the gas diffusion layer (GDL). The solution works if the cell current density is below 100 mA cm(-2). Fitting the model impedance to the experimental spectrum gives the ORR Tafel slope, the double layer capacitance, and the transport parameters of the CCL and GDL.