Solubility of NH4VO3 and CO(NH2)(2) in aqueous solutions within a temperature range of 293-323 K was measured employing the isothermal solution saturation method. These results were used to plot part of the polythermal solubility surface for the NH4VO3 + CO(NH2)(2) + H2O system. Additionally, the solution density dependence versus the urea concentration expressed in mole fraction was presented. Compound formation did not occur.