YVO4:Bi3+,Eu3+ nanoparticles were prepared by the wet chemical synthesis in various concentrations of sodium citrate, 15 <= x(cit)<= 90, where x(cit) is the nominal molar percentage of citrate relative to the sum of metallic ions, Y3+, Bi3+, and Eu3+. Mean primary nanoparticle diameter and mean hydrodynamic size in the aqueous colloidal solution have minimum values, 21 and 36 nm, respectively, for the sample prepared at x(cit)=50. The transparency of the aqueous colloidal solution in the visible region increases with decreasing the mean hydrodynamic size, and the sample prepared at x(cit)=50 shows the highest transparency. YVO4:Bi3+,Eu3+ nanoparticles show the characteristic photobleaching behavior and the photoreduction of V5+ to V4+ under the irradiation of near-UV light, where the fraction of photobleach becomes larger at large x(cit). These results suggest that the citrate ion works not only as an effective dispersion agent, but also as a reducing agent against V5+ of YVO4:Bi3+,Eu3+.