Polymer electrolyte membrane fuel cells (PEMFCs) are a good candidate for fuel cell electric vehicles (FCEVs) due to their high efficiency, high power density and zero-emission. However, the lifetime is one of the main barriers to overcome before their commercialization. The durability testing methods for PEMFCs are main include electrocatalyst cycle, catalyst support cycle, membrane electrode assembly (MEA) chemical stability, membrane mechanical cycle and so on. In addition, there is little research about MEA chemical stability test, which applies a continuous open-circuit voltage (OCV) to produce more free radicals and these will have a bad influence on PEMFCs. Based on this, the durability of PEMFC was studied under OCV operation at 30% relative humidity (RH), 90 °C and 150 kPa inlet pressure. The electrochemical performances such as in-situ cyclic voltammetry (CV), linear sweep voltage (LSV) and cell polarization were used to evaluate the durability of PEMFC. Scanning electron microscopy (SEM) was applied to identify the degradation of polymer electrolyte membrane (PEM). After 168 h of durability test, the open circuit voltage decreases from 0.96 to 0.8 V, the maximum power density decreases from 795 to 470 mW cm-2 and the current densities exceed or close to 15 mA cm-2. Apart from this, the reduction in thickness of PEM is 4 μm. These results indicate that the free radicals, which are produced during the OCV test can degradation the ionomer and cause thinning PEM. Eventually lead to bad electrochemical performance and poor lifetime of PEMFCs. Therefore, it is necessary to develop free-radical scavengers to improve the durability of the PEMFCs.