Abstract: Liquid-liquid equilibrium data were measured for the binary systems of water-octylenic aldehyde and water-n-butanol under atmospheric pressure. Also the vapor-liquid equilibrium data under 26.66kPa pressure for n-butanol-octylenic aldehyde binary system and water-n-butanol-octylenic aldehyde ternary system were determined. From the equilibrium data determined for the above three binary systems, the NRTL constants and regular parameters are obtained and the VLE for the ternary system are predicted with the constants and parameters. A comparison of the predicted values with those measured shows satisfactory results. The liquid-liquid equilibrium and vapor-liquid equilibrium are unified in the correlation in this work.