In this study, spherical Se nanoparticles were prepared by the reduction of aqueous selenious acid with ice bath through a simple, conventional, one-step method without the aid of any surfactant, or template. The nanoparticles were characterized by transmission electron microscopy (TEM), photon correlation spectroscopy (PCS), X-ray powder diffraction (XRD), Ultraviolet-visible spectroscopy (UV-vis), Zeta potential, respectively. The results show the Se nanoparticles have good particle dispersion with the average diameters of 36 nm and are amorphous (alpha-Se). Tablets A and B containing dextran and Se nanoparticles were synthesized with different preparation methods. Se nanoparticles studded equably in the interior the surface of the tablets, and there are strong interactions between Se and dextran. The release of Se from tablets is investigated in the gastric and intestinal conditions. It is found that the pH environment and different synthetical methods have significant influence on the release rate of Se. The release mechanism of Se nanoparticles is also discussed. The nanocomposites can be applied in controlled releasing of Se nanomedicine. (c) 2008 Elsevier B.V. All rights reserved.