The effect of atomic oxygen (AO) on the surface oxidation of several typical Cu-based bulk metallic glasses (BMGs) was studied in the present work. The AO source using in this study is generated by discharge plasma type ground simulation equipment. The AO erosion/oxidation resistances of the amorphous alloy samples were assessed based on the analysis of mass loss, surface color and microstructure. It is found that these Cu-based BMGs possess good AO erosion/oxidation resistance and their resistance to AO erosion/oxidation strongly depends on the chemical composition. For the samples containing more Ag and/or Cu, the AO erosion/oxidation resistance is weaker. The present result is important for designing new metallic glasses using as space materials. The presence of atomic oxygen (AO) in low Earth orbit (LEO, altitude from ~200 to ~700 km) is one of important reasons for surface degradation of the aerospace materials. Atomic oxygen, which possesses high chemical activity, is the dominant chemical constituent (80%) in the neutral atmosphere in LEO [1]. When the spacecraft locates in LEO with an orbital velocity of 7-8 km s, AO impacts the surface of the spacecraft with a kinetic energy of ~5 eV, thus can react with many elements [2]. Then, it may lead to surface erosion and property degradation of space materials which would further affect the safety/longevity of spacecrafts. Therefore, studies on the AO effects have been widely appreciated. Through testing platforms equipped in spacecrafts and all kinds of ground effect simulation testing devices, a large number of aerospace materials such as polymer [3], inorganic material coating [4,5], silver [6], aluminum [7], titanium [8] and carbon materials [9], etc., have been studied extensively. For most metal materials, AO will react with them to form oxidized film which can prevent further oxidation to erode the material. Except AO sensitive elements such as Os, Ag and Cu, metal materials usually have relatively better AO resistance than those polymers and carbon materials. But the films generated by AO can result in a change in surface roughness and thus leading to degradation of luminous reflectance, frictional wear properties and even welding performance [7]. Therefore it is of great interest to investigate the effect of AO on metallic materials to better understand the oxidation mechanism. So far, the field of AO erosion study is largely focused on crystalline materials. Recent decades, bulk metallic glasses (BMGs), new comers of metallic materials, have attracted lots of attention [10][11][12][13][14] due to excellent mechanical and functional properties [15][16][17][18][19][20][21], which are believed to be resulted by their unique structure [22,23]. Since high performance of BMGs make them potential candidates of space materials, their AO erosion resistance is of interest to be investigated.The main aim of the present work is to explore the influence of Cu or Ag contained on the AO resistance of BMG materials. To our knowledge, those alloys containing elements ...