Two unsaturated polyesters based on maleic anhydride, phthalic anhydride, and sebasic acid with each of linear 1,6-hexanediol (PEL) and cyclic 1,4-cyclohexanediol (PEC) were prepared. Their structures were characterized by IR and H-1 NMR spectra. Their composites were prepared by mixing different ratios (60, 70, and 80%) with talc and kaolin with polyester/styrene mixture. The effect of linear and cyclic glycols and the effect of filler type and concentration of these composites were studied in terms of their electrical properties and the hardness before and after aging. The thermal behavior of styrenated polyesters and their composites was studied using thermogravimetric analysis. It has been found that both fillers increase the thermal stability and decrease the weight loss. The permittivity epsilon ' and the dielectric loss epsilon '' were measured in the frequency range 100 Hz up to 100 kHz at room temperature 25 degrees C +/- 1. The polyester composite samples containing 70% filler lead to good electrical properties in addition to its resistance to thermal aging. The hardness value was increased by increasing the filler content before and after aging. The polyester composites based on cyclic glycol and loaded with 80% kaolin gave the highest hardness values. (C) 2008 Wiley Periodicals, Inc.