Poly(styrene butylacrylate) latex/nano-ZnO composites were prepared by blending poly(styrene butylacrylate) latex with a water slurry of nano-ZnO particles, and the effects of certain parameters, such as particle size, dispersant type, dispersing time and others, on the dispersibility, mechanical properties, ultraviolet (UV) shielding and near infrared (NIR) shielding were investigated with transmission electron microscopy (TEM), an Instron testing machine, dynamic mechanical analysis and ultraviolet-visible-near infrared (UV-VIS-NIR) spectrophotometry. TEM observation showed that dispersants with long chains are better than those with short chains at enhancing the dispersibility of nano-ZnO particles in a matrix; extending dispersing time also improves the dispersibility of nano-ZnO particles in a matrix. Instron tests showed that the nanocomposite polymers embedded with nano-ZnO particles had much higher tensile strength than the corresponding composite polymers with micro-ZnO particles. As the nano-ZnO content increased, the temperature of glass transition (T-g) of the nanocomposite polymer embedded with 60 nm ZnO particles first increased then decreased, but 100 nm ZnO and micro-ZnO particles seemed to have no influence on the T-g of the composite polymers. The better dispersibility of nano-ZnO particles resulted in higher T-g values. Increasing nano-ZnO content or dispersibility could enhance the UV shielding properties of the nanocomposite polymers, and 60 nm ZnO particles could more effectively shield UV rays than 100 nm ZnO particles. Micro-ZnO particles basically had no effect on the UV absorbance of the composite polymers. A blue-shift phenomenon was observed at 365 nm when nano-ZnO particles were present in the nanocomposite polymers. NIR analysis indicated that as nano-ZnO content increased, the NIR shielding of the nanocomposite polymers increased, but the NIR shielding properties seemed to be more influenced by particle size than by the nano-effect. (C) 2003 Wiley Periodicals, Inc.