nanoparticles were prepared by the wet chemical synthesis in various concentrations of sodium citrate,, where is the nominal molar percentage of citrate relative to the sum of metallic ions,,, and. Mean primary nanoparticle diameter and mean hydrodynamic size in the aqueous colloidal solution have minimum values, 21 and, respectively, for the sample prepared at. The transparency of the aqueous colloidal solution in the visible region increases with decreasing the mean hydrodynamic size, and the sample prepared at shows the highest transparency. nanoparticles show the characteristic photobleaching behavior and the photoreduction of to under the irradiation of near-UV light, where the fraction of photobleach becomes larger at large. These results suggest that the citrate ion works not only as an effective dispersion agent, but also as a reducing agent against of.