Abstract:This study is about the effect of nitrogen gas pressures during manufacturing process on the mechanical properties of composite materials. TiO 2 /epoxy resin nanocomposites and carbon fiber reinforced epoxy resin(CFRP) composites were fabricated under various nitrogen gas pressures. Tensile strength test, vicker's hardness test and fracture surface observation were carried out to investigate the effect of nitrogen gas pressure. As a result, the tensile strength of nanocomposite and CFRP composites showed clearly increasing tendency by a change in the nitrogen gas pressure up to 3.0 atm and then the tensile strength decreased a little.However, the vicker's hardness of TiO 2 /epoxy nanocomposites showed same hardness values regardless of the nitrogen gas pressures.