A transparent colloidal solution of YVO4:Bi3+,Eu3+ nanophosphor is prepared by the wet chemical synthesis in the presence of sodium citrate. When an ethylene glycol solution of Bi(NO3)3, aqueous solutions of (Y,Eu)(NO3)3, sodium citrate, and Na3VO4 are mixed and aged at 85 °C, crystalline YVO4:Bi3+,Eu3+ spherical nanoparticles of ∼ 20 nm in size are formed via the amorphous precursor during aging, as confirmed by X-ray diffractometry and transmission electron microscopy. The crystallization completes at the aging time of ∼ 25 min. At the same time, a sudden reduction in the hydrodynamic size is observed by dynamic light scattering analysis, and the colloidal solution becomes transparent to naked eyes. The nominal molar percentage of sodium citrate relative to the sum of metallic ions, Y3+, Bi3+, and Eu3+, affects the particle size and the aggregation property of the nanoparticles. The sample prepared at 50 mol% citrate, followed by aging at 85 °C for 60 min have the minimum mean size of primary nanoparticles, 21 nm, the minimum mean hydrodynamic size, 36 nm, and hence the highest transparency.