The solubility of KVO3 in water + ammonia solutions was determined within the temperature range of 293-323 K by employing the isothermal solution saturation method. The initial concentration of NH3 in solution varied between 1 and 6 mol.dm(-3). The density of the equilibrated solutions was also determined. The data presented herein are essential for the assessment of optimum operating conditions for the production process of potassium carbonate introducing the modified Solvay method.