Polymer nanocomposites are usually made by incorporating dried nanoparticles into polymer matrices. This way not only leads to easy aggregation of nanoparticles but also readily brings about opaqueness for nanocomposites based on functionally transparent polymers. In this letter, transparent ZnO/epoxy nanocomposites with high-UV shielding efficiency were prepared via two simple steps: first, in situ preparation of zinc hydroxide (Zn(OH)2)/epoxy from the reaction of aqueous zinc acetate (Zn(Ac)(2)center dot 2H2O) and sodium hydroxide (NaOH) at 30 degrees C in the presence of high-viscosity epoxy resin; second, thermal treatment of the as-prepared Zn(OH)2/epoxy hybrid into ZnO/epoxy composites. Optical properties of the resultant ZnO/epoxy nanocomposites were studied using an ultravioletvisible (UVvis) spectrophotometer. The nanocomposites containing a very low content of ZnO nanoparticles (0.06 wt %) possessed the optimal optical properties, namely high-visible light transparency and high-UV light shielding efficiency. Consequently, the as-prepared ZnO/epoxy nanocomposites are promising for use as novel packaging materials in lighting emitting diodes technology. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012