This paper presents the development of dynamic models for proton exchange membrane (PEM) fuel cells using electrical circuits. The models have been implemented in MATLAB/SIMULINK and PSPICE environments. Both the double-layer charging effect and the thermodynamic characteristic inside the fuel cell are included in the models. The model responses obtained at steady-state and transient conditions are validated by experimental data measured from an Avista Labs SR-12 500-W PEM fuel-cell stack. The models could be used in PEM fuel-cell control related studies.