Vapor-liquid equilibrium (VLE) data for ternary system of α-pinene(1) + β-pinene(2)+ p-cymene(3) were measured at 53.3 kPa and 80.0 kPa using the modified Dvorak-Boublik equilibrium still. The experimental data of ternary systems were found to be thermodynamically consistent by the McDermott-Ellis method. The ternary system data at reduced pressure were predicted with the parameters of NRTL model obtained from the pertinent binary systems. The maximum absolute deviations in temperature at two pressures were 0.80 and 0.86 K respectively

average absolute deviations were 0.30 and 0.39 K respectively. The ternary absolute deviation and average absolute deviation in vapor-phase mole fraction of α-pinene were 0.0096 and 0.0033 respectively

and those of β-pinene were 0.0102 and 0.0028 respectively at 53.3 kPa. The max absolute deviation and average absolute deviations in vaporphase mole fraction of α-pinene were 0.0083 and 0.0049 respectively

and those of β-pinene were 0.0081 and 0.0025 respectively at 80.0 kPa. These results provide the basis data for the separation of main components of turpentine.