The existence of non-stoichiometric solid-solution phase in YVO4 has been examined by the compositional variations in the lattice parameters and the photoluminescence intensities. The lattice parameters, c-axis, a-axis and c/a ratio, and the photoluminescence intensities (lambda=440 nm) vary apparently with the vanadium content of the sintered YVO4 specimens. A vanadium deficient non-stoichiometric solid-solution ranging from about 48 to 50 mol% of vanadium content is suggested to be formed by the generation of vanadium vacancy.