The various hazards in the low earth orbit space cause damage mostly on the exposed surfaces of polymer-based materials. Neutral particles, especially atomic oxygen, erode the exposed surface, and cyclic temperature variation produces microcracks that degrade mechanical performance. To protect substrate materials from the harmful environments, this research investigated the protective effect of nanocomposite film under a simulated low earth orbit space environment involving 4x10(-4)torr high vacuum, 200nm ultraviolet radiation, 14 thermal cycles ranging from -70? to 100?, and atomic oxygen flux of 2.07x10(14)atoms/cm(2)s. The protective films of multi-walled carbon nanotubes or nano-silica dispersed in epoxy matrix were fabricated using a comma roll casting machine. The physical and mechanical changes of the film-protected specimens under the simulated low earth orbit environment were compared to those of no-film-protected specimens. The amount of specimen erosion during the low earth orbit simulation test was analyzed through mass change. Furthermore, the tensile performance before and after exposure to the simulated low earth orbit environment was evaluated. Since the uniformly dispersed nano-silica blocked the attack of atomic oxygen and ultraviolet radiation, and internal multi-walled carbon nanotubes impeded crack propagation due to the bridging effect, the specimens protected by nanocomposite film showed less damage on the exposed surfaces and smallest in degradation of tensile strength after exposure to the simulated low earth orbit environment.