Using the hydrothermal method, we synthesized water soluble YVO4: Yb, Er nanoparticles with a size less than 10 nm. Nanoparticles exhibit intense luminescence in the green region due to Er 3+ ions when excited by laser radiation at a wavelength of 980 nm as a result of the upconversion process. Bright and stable luminescence also persists in an aqueous solution of nanoparticles. Based on experimental data, it can be argued that the objects obtained are promising in biological applications, as well as up-conversion phosphors.