Poor durability of polymer electrolyte membranes is one of the most limiting factors of proton exchange membrane fuel cell (PEMFC). Hydrogen peroxide which is formed electrochemically or chemically during operation is one of the potential deteriorating factors, particularly for polyaromatic membranes. To be able to increase membrane durability, the aging path involved must be elucidated. To give an insight into the degradation mechanism of sulfonated polyaryl ether ketones (sPAEK) a study on model compound has been performed. Each species produced has been collected by liquid chromatography and identified by NMR, IR and mass spectroscopies. We have demonstrated that degradation proceeds through the addition of a hydroxyl radical on the aromatic ring. Then, the oxidation of these phenolic groups leads to several chain scissions. On the basis of these experiments, a strategy can be drawn to improve the membrane durability. (C) 2009 Elsevier Ltd. All rights reserved.