The solubility of ammonium bicarbonate and ammonium vanadate in the NH4HCO3 + NH4VO3 + H2O system has been investigated at 293 K to 323 K. A polytherm section of the system has been drawn. The change of mutual salt concentrations and the density of the solutions as a function of the temperature have been described by the appropriate equations. The equations can be used for the detailed calculations of the NH4HCO3 concentration and the density of the solutions for any temperature within the investigated range.