A recirculating still specially designed for partially miscible systems was used for the determination of isobaric vapor-liquid equilibrium data at 760 mm Hg for the n-butanol-isobutanol-water system. For the determination of solubility at the boiling point the cloud point titration method was used. The vapor-liquid phase equilibrium data and solubility data at boiling point for the ternary system under study have been well correlated by the modified Wilson equation proposed by Mitsuyasu. The NRTL and the Uniquac equations were also used for the correlation of the vapor-liquid phase equilibrium data. All the above correlations are adequate for design purposes.