Particulate polymer composites of Isophthalate based unsaturated polyester resin filled with different concentrations of lead monoxide were prepared. These composites were investigated for physical, thermal, mechanical, and gamma radiation shielding characteristics. The results of density evaluation, microscopic studies, and the radiation shielding properties for gamma rays of energy 0.662 MeV from Cs-137 point source have been presented in this article. The results show that, the density of the composites was observed to increase with filler loading. The morphological analysis of the composites made using the scanning electron microscope showed that, the lead monoxide particles were observed to disperse uniformly in the polymer matrix with an average inter particle distance of about 10 pm and an average size of about 5.36 mu m. The linear attenuation coefficient of the composites was found to increase with increased filler content in the composites. The highest value of 0.206 cm(-1) was found for 50 wt % of lead monoxide. These composites were observed to exhibit excellent % of heaviness and Half value layer in comparison with other conventional materials. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 1503-1508, 2009