The solubility of sodium vanadate and sodium nitrate was investigated in the NaVO3-NaNO3-H2O system at the temperature range 293-323 K, with the method of isothermal saturation of a solution. The obtained results gave a basis for the plot of a fragment of the solubility isotherm for the investigated system. That system is a part of the five-component NH4NO3-NaVO3-NH4VO3-NaNO3-H2O system and is necessary for plotting the solubility isotherm in the projection according to Janecke method. Knowledge of the course of that isotherm for the five-component system is necessary for determination of the optimal conditions for utilization of the postfiltration liquor from the soda production from NaNO3 by the Solvay method with the use of NaVO3.