Degradation of PEMFC performance under dynamic loading cycling situation was studied by simulating automotive working conditions. A protocol of driving cycle was set up. Each driving cycle was consisting of six different periods. The performance of the fuel cell during driving cycle periods was represented by time-dependent voltage profiles. Polarization curves, measured in regular intervals, revealed a changed degradation rate in different operation periods. A rapid degradation of performance could be observed after 280 h of operation. In contrast to the starting conditions of the MEA, the degradation of membrane and dissolution and aggregation of catalysts were clearly visible at the end of testing. Furthermore, after 370 h of testing, Pt was not uniformly dispersed in the catalysts layer and some also scattered in the membrane. Cracks and gaps appeared in the catalyst layer. This change of micro-structure corresponded to the loss of electro-chemical active area of the MEA and the increased membrane resistance and charge transfer resistance. (c) 2008 Published by Elsevier Ltd on behalf of International Association for Hydrogen Energy.