A significantly challenging issue in polymer electrolyte fuel cells (PEFCs) is the insufficient durability of the membrane electrode assembly (MEA) electrodes caused by crack formation and growth. A decrease in interconnections of the electrical pathways in the electrodes leads to poor performance and durability of the PEFCs. Therefore, fundamental understanding of the nature of the crack formation and growth in electrodes is critical for improving fuel cell durability. In this study, an electromechanical diagnostic method is proposed to monitor the cracks in the PEFC electrodes. The electrical resistance of electrode is measured through the in situ four-wire electrical resistance measurements under tension. The crack areal density is proposed and measured as a quantitative parameter to define the presence of cracks in the electrodes using an optical microscope. It is found that the change of electrical resistances under tension increases with the electrode thickness (i.e., Pt loading), which results from the crack growth in the electrodes. This electromechanical diagnostic method is useful for understanding the crack mechanics consisting of initiation, propagation, and widening stages, and expected to facilitate the design of robust electrodes for highly durable fuel cells. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.