ZnO nanoparticles were prepared by a chemical solution method using the reaction between Zn(CH3COO)(2)center dot 2H(2)O and LiOH center dot H2O in an ethanol solvent. A dialyzing treatment of the resultant chemically impure nanoparticles was introduced in the present work, aiming at increasing their chemical purity in terms of adsorbed species. The progress of dialysis was monitored with electrical conductivity of dialysate. X-ray diffraction analysis and Fourier transform infrared spectroscopy were employed to check the chemical purity of the ZnO nanoparticles after the dialyzing treatment. Furthermore, the dialyzed ZnO nanoparticles were utilized to fabricate ZnO/SiO2 nanocomposite thin films by a sol-gel method with a dip-coating technique. Stable coating solutions were obtained only with the dialyzed ZnO nanoparticles, which also indicated their chemical purity. The nanocomposite thin films exhibited a unique optical property with antireflection against visible light and photoluminescence under irradiation with ultraviolet light.