Fatigue behavior of Epoxy/ SiO2nanocomposites with different volume fraction of SiO2nano particles (1%,3%,5%,7% and10%) are reported , Atomic force microscopy techniques(AFM) was used with scanning probe microscope to measure the particles size of SiO2 nanoparticales.Minimum roughness of the composites was found for composites with 3% vol.fraction of SiO2 nanoparticles.Epoxy/SiO2 nanocomposites were reinforced with 6 layers of chopped mat E-glass fiber and their fatigue behaviourare reported.Fatigue test was carried under rotary bending method and the type of loading was sinusoidal wave with wave ratio R=-1,and loading frequency 5Hz,which is believed to give a negligible temperature rise during the test.Values of fatigue strength ,fatigue life and fatigue limit of the tested composites from S-N curves are reported.The results show that addition of SiO2 nanoparticle enhance the fatigue values however more enhancement was obtained for Epoxy/SiO2 nanocomposite reinforced with 6 layers of chopped mat E-glass fiber.