Abstract Tungsten Trioxide nanoparticles with various weight fraction filled epoxy composites were fabricated to investigate their effect on three mechanical properties, flexural strain, flexural modulus, impact, and hardener test. The test conducted at room temperature and the results show an enhancement in the mechanical properties of the reinforced epoxy matrix compared to the pure epoxy resin. Flexural modulus increased with increasing of Nano filler content up to 2 wt% and then decreased. Hardness increased with increasing of the filler content rang (1–3) wt%. Impact strength and fracture toughness increased with increasing of the filler content. Nano crystalline structure of the commercial WO3 was confirmed employing powder X-ray diffraction analyser.