Abstract: Atomic oxygen (AO) is prevalent in Low Earth Orbit (LEO). Ground-based testing on AO exposure was performed to investigate the effects of atomic oxygen on materials to be used in LEO spacecraft. Two types of adhesive materials, E-32 epoxy and GS414 silicone, were tested in the atomic oxygen testing facility at Beijing Institute of Spacecraft Environment Engineering (BISEE). The equivalent atomic oxygen fluence in test was approximately 1.4×1021 atom/cm2 as determined based on two years’ exposure on LEO. Significant mass losses of the epoxy adhesive samples were observed after the exposure to atomic oxygen, but relatively small mass changes were found in the silicone samples. The erosion yields of epoxy samples range from 3.2×10-24 cm3/atom to 3.8×10-24 cm3/atom. Bleaching by atomic oxygen was found in the epoxy samples. The surface on the silicone sample was glossed after AO exposure. The external appearance of both kinds of materials was analyzed using Scanning Electron Microscope (SEM) and X-ray Photoelectron Spectroscopy (XPS). A comparison between unexposed and exposed samples shows noticeable changes on the surface of materials.