This paper presents the effect of five dissolved salts (sodium chloride, calcium chloride, zinc chloride, cadmium chloride, and ammonium chloride) on the endothermic enthalpy of mixing of the binary system 1,4-dioxane + formic acid measured at 303.15 K using an isothermal displacement calorimeter with vapor space. The salt sodium chloride increases the excess enthalpy values to an extent. A significantly increasing trend in excess enthalpy values for the salt calcium chloride, a remarkably decreased excess enthalpy for the salt ammonium chloride, and a comparatively smaller decrease in the excess enthalpy with the addition of zinc chloride and cadmium chloride were noticed. The experimental values of the enthalpy of mixing were fitted into a modified Redlich-Kister equation, and the deviations and parameters are reported. While the excess enthalpies of mixing (H-E) are more positive for the salts sodium chloride, cadmium chloride, and ammonium chloride, those for the salts calcium chloride and zinc chloride are more negative with increasing salt concentrations which exemplify the importance of solute-formic acid interaction.