In this study, lead oxide nanorods were synthesized without surfactants in an aqueous medium at room temperature Different percentages of lead oxide nanorods were added to an unsaturated polyester polymer matrix to have various wt% nanocomposites. The gamma-ray mass attenuation coefficients were measured as a function of the weight percentages of lead oxide at different thicknesses. This was done with radioactive source Ra-226. The unsaturated polyester/lead oxide nanorods composite was treated with 1, 2.5, 5, 10, 15, 20, 40, and 60 wt% lead oxide nanorods, as different proportions of the filler. According to the results, the best radiation attenuation was for 60 wt% nanocomposite. In such a nanocomposite, the optimal half value layer, tenth value layer, and mean free path were about 2.4, 7.6, and 3.35 cm, resp.