Positron annihilation techniques have been investigated as useful tool in studying the degree of interfacial interaction of nanoparticles surface and the polymer chains. Positron annihilation spectroscopy was very sensitive to the molecular motions of the polymer chains. Hence,it was used to measure the glass transition temperature of the polymer nanocomposites. In addition, positron annihilation spectroscopy was successfully used to study the free volume properties of the polymer nanocomposites.