The long term stability and durability of gaskets made of silicone rubber in proton exchange membrane fuel cell (PEMFC) has important effect on the sealing and the electric-chemical performance of the fuel cell. In present paper, the time-dependent chemical degradation of a silicone rubber was studied in three simulated PEMFC environments. The test temperature was selected and used at 90°C in this study according to the actual PEM fuel cell operation. Optical microscopy was used to show the topographical changes on the sample surface. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was employed to study the surface chemistry of the gasket material before and after exposure to the simulated PEM fuel cell environments over time. The results show that the weight loss increased with the exposure time for the samples. Optical microscopy reveals that the surface conditions of the samples changed over time from initially smooth to rough, crack appearance and finally crack propagation. The ATR-FTIR results show that the surface chemistry changed significantly via de-crosslinking and chain scission in the backbone for the material over time.