Long-term stability and durability of gaskets in Proton Exchange Membrane (PEM) fuel cell are important to both sealing and the electrochemical performance of PEM fuel cells. In this paper, the time-dependent aging process of silicone rubber, which is one of the potential gasket materials for PEM fuel cells, is investigated in one simulated PEM fuel cell environment and three accelerated durability test (ADT) media at 70 degrees C. Optical microscopy is employed to observe the topographical changes on the surfaces of samples. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) are used to study the surface chemistry of the samples before and after exposure to the test environments over time. The optical microscopy results indicate that the surface conditions of the samples change from initially smooth to rough, crack appearance and finally crack propagation. The AIR-FTIR and XPS results reveal that the degradation mechanisms of the silicone rubber are likely due to the de-crosslinking and chain scission in the backbone, and the acid has a significant effect on the degradation. (C) 2012 Elsevier B.V. All rights reserved.