Multi-walled carbon nanotube (MWNT)/epoxy composites were fabricated with different nanotube weight percent (wt.%) concentrations. Ultra-sonication and homogenization were simultaneously used to uniformly disperse MWNTs into the epoxy. The MWNT/epoxy composites were tested in simulated low earth orbit (LEO) environment. Effects of MWNTs content on space environment characteristics of the nanocomposites were studied herein. The LEO space environment simulation was characterized by high vacuum (~10-5 Torr), ultraviolet (UV) radiation (<200nm wavelength), temperature cycling (-70ºC~100ºC), and atomic oxygen atmosphere (AO flux of ~1016 atoms/cm2·s and kinetic energy of ~0.04 eV). The tensile properties as well as mass loss of the nanocomposites with various nanotube concentrations, exposed to the simulated LEO environment, were investigated. The surface morphology of MWNT/epoxy nanocomposites under space environmental effects was observed by scanning electron magnetoscope (SEM).