Experiments were conducted with an IFM ground equipment to investigate the effect of atomic oxygen on silicone rubber O-rings. By measuring the pressure between two O-rings, leakage rates between the two O-rings before and after exposure to atomic oxygen were compared. In addition, the surface characteristics of O-ring were analyzed by scanning electron microscope. All experiments provethat atomic oxygen erodes the surface of O-ring seriously, resulting in a weight loss and a weakened sealing capacity of the O-ring. The results show that the surface damage, the weight loss and the leakage rate of an O-ring all increase in proportion to its of the time exposed to atomic oxygen.