Abstract: The effect of low earth orbit (LEO) atomic oxygen (AO) on spacecraft materials is reviewed in this paper. Firstly, the mechanism of AO interaction with space materials and the related hazards are briefly discussed. Then, particular emphasis is put on the AO interactions with metals, such as with Al, Ag, Cu, Ni, and semi-conductive materials. Finally, the techniques of AO protection as well as the related results on the AO resistance of various materials are summarized.