The vapor-liquid equilibrium of the system water-nitric acid has been described. The activity coefficients in the liquid phase are evaluated according to a new model. This model combines the effect of the long range forces expressed by a Debye-Huckel contribution on a mole fraction basis, with the effect of short range forces expressed by a virial expansion of the NRTL equation. The proposed model can be used to describe the vapor-liquid equilibrium of the system water-nitric acid from 20 to 120 degrees C over the entire concentration range.