Abstract: In this part all the data, including the isothermal vapor pressure-liquid composition data for acetone isobutyraldehyde binary and the mutually miscible region of the acetone-isobutyraldehyde-water ternary and the liquid-liquid-vapor equilibrium data for isobutyraldehyde-water binary have been reported. With the aid of a statistical method for testing the thermodynamic consistency, experimental vapor liquid equilibrium results reported by K. Kojima are raw data for acetone-water binary.With a maximum likelihood method, the binary parameters of NRTL and UNIQUAC models for all the three binaries are estimated by fitting the experimental data. The vapor pressures of the ternary system in the mutually miscible region predicted from these binary parameters are in good agreement with the experimental results.