Abstract: Nanocomposite was prepared by nanometer TiO₂ and epoxy resin. The affects of the content of nanometer TiO₂ on the properties of the nanocomposite were studied. The dispersion of TiO₂ was observed with TEM. The data of the free volume were studied by the positron annihilation technique. As a result, the tensile strength ,modulus and impact strength of the epoxy resin were increased with the dispersion of nanometer TiO₂. The free volume length of the epoxy resin was increased with nanometer.