In this study, the gamma-ray shielding performance and the mechanical properties of waterborne polyurethane (WPU) composites embedded with tungsten trioxide (WO3) and bismuth trioxide (Bi2O3) were investigated. The results indicated that the shielding properties of the composites against gamma rays increased with WO3/Bi2O3 loading and that nanocomposites were better able to attenuate gamma rays than microcomposites. The mass ratio of WO3 and Bi2O3 in the composite played an important role in attenuating low-energy gamma rays. With the increment of Bi2O3 loading, the composite’s ability to attenuate 59.5 keV and 121.8 keV gamma rays improved, whereas higher WO3 contents enhanced the ability to attenuate 81 keV gamma ray. In terms of mechanical properties, with WO3/Bi2O3 loading increased, the tensile strength of composites frst increased and then decreased, and the elongation at break steadily decreased. Gamma irradiation also improved the mechanical properties of the WPU composites, as indicated by the increase in tensile strength as the irradiation dose increased from 50 to 200 kGy.