Formic acid and water form a maximum-boiling azeotrope in their mixtures. To break the azeotropic boiling in this system, inorganic salts are frequently added, because the addition of electrolytes alters significantly the equilibrium nature of the original system. In this paper we report the vapor-liquid equilibrium data for the formic acid-water-magnesium chloride system over a wide range of salt concentrations at 760 mmHg. On the pseudo-binary assumption the equilibrium data were correlated with Hala's model for liquid phase, by considering the chemical equilibrium in vapor phase. The model showed an excellent agreement with experimental data over a broad range of salt concentrations.