The durability of high temperature proton exchange membrane (HT-PEM) fuel cells is very important for its long term performance and commercialization. Commercialization demands progress, especially in the development of fuel cell catalyst materials and carbon supports. The role of platinum and carbon in the catalytic layer are crucial for the stable performance of a fuel cell. Potential cycling is used to evaluate the stability of platinum and carbon support material of catalyst layer. Fuel cells operated under cycling conditions have lower durability than those operated under steady state conditions. The aim of this work is to study degradation of phosphoric acid doped polybenzimidazole membrane based fuel cell under accelerated potential cycling conditions. Potential cycling degrades fuel cell performance. Understanding this degradation related issues associated with potential cycling is necessary to improve the durability of HT-PEM fuel cell. The fuel cell is cycled between open circuit voltage and 0.5V for 6 minutes per cycle (as represented in figure 1) until 5000 cycles. The performance of fuel cell is characterized using polarization curves, electrochemical impedance spectroscopy, cyclic voltammetry and linear sweep voltammetry at beginning of life and after the accelerated degradation test to investigate the effect of change in potential step from open circuit voltage to operating voltage of 0.5V. Cathode exhaust is monitored for carbon dioxide using real time infra-red spectroscopy and the condensed water is analyzed for phosphoric acid. Material characterization methods are used to evaluate the degradation mechanisms responsible for the observed performance loss.