The solubility of the (NH4)(2)C2O4-NH4VO3-H2O system has been measured over a temperature range from 313.15 to 363.15 K. On the basis of the results, a solubility diagram has been drawn. Additionally, the densities of the solutions have been measured. From analysis of the solubility data, a separation method for NH4VO3 from the (NH4)(2)C2O4-NH4VO3-H2O system was proposed, involving cooling and salting-out crystallization from (NH4)(2)C2O4 solution.