The development of nanocomposite materials has caught increasing attention due to their wide range of potential applications. Because of its significant optical properties, zinc oxide (ZnO) has been selected to mix with polymers as a highly efficient ultraviolet (UV) absorber. In this study, ZnO/low density polyethylene (LDPE) nanocomposites were prepared by melt mixing. The UV-visible absorbance of the nanocomposites with various ZnO concentrations was measured, and compared to the corresponding optical properties of submicron ZnO filled LDPE composite. The dispersion of ZnO nanoparticles in an LDPE matrix was studied by field emission scanning electron microscopy. It was observed that the dispersion of nanoparticles was greatly improved by drying the nanoparticles at high temperature (200 ^oC) under vacuum before mixing. In addition to the drying process, the dispersion of nanoparticles was also affected by the ZnO concentration in the nanocomposite and the mixing conditions. The UV-visible absorbance of the polymer nanocomposite was found to depend on the loading of ZnO nanoparticles as well as on the resultant particle dispersion. It was observed that the addition of ZnO nanoparticles enhanced the UV absorbance of the polymer dramatically. In the visible wavelength range, the absorbance of the nanocomposite increased with increasing the ZnO nanoparticle concentration, because of the agglomeration of ZnO nanoparticles. At low ZnO concentrations (1–2 wt %), optical transparency can be achieved in the ZnO/LDPE nanocomposites, which is highly desirable for packaging materials. In comparison, submicron ZnO filled LDPE composite showed less efficient UV absorbance and lower optical transparency. This work was supported by Sealed Air Corporation and the Nanoscale Science and Engineering Initiative of the National Science Foundation under NSF Award Number DMR-0117792.