This work is concerned with the preparation and characterization of composite materials prepared by molding a mixture of filler and styrenated polyesters. Positron annihilation spectroscopy (PAS) coupled with electrical and mechanical measurements have been used to investigate the effect of different fillers such as Cu, Al and Zn on some properties of styrenated polyesters. It has been found that, the permittivity (epsilon'), dielectric loss (epsilon'') and the conductivity (sigma) increase by increasing the Cu and Al content in the two styrenated polyesters (PE1and PE2) while no significant effect is noticed in case of Zn content. On the other hand, the 10% as well as 20% of filler content is found to be an onset point at which a change in the variation trend of tensile strength and hardness occurs. Furthermore, the free-volume hole size (V (h)) and its concentration (f) showed a decrease with increasing the amount of filler, except at 10% filler V (h) showed an increase. These variations were interpreted in terms of the free-volume distributions and the correlation of free-volume parameters with conductivity (sigma) and hardness.