Vapor-liquid equilibrium (VLE) data for the associating ternary system propanal + propanol + propanoic acid and three constituent binary systems were determined at different liquid phase compositions using a novel pump ebulliometer at 101.325 kPa. The vapor-phase compositions of these binary systems were calculated from Tpx according to the function of molar excess Gibbs energy by the Barker's method. Moreover, the experimental T, x data are used to estimate Wilson, nonrandom two-liquid (NRTL), Margules, van Laar, and universal quasichemical activity coefficient (UNIQUAC) model parameters from regression, and these parameters in turn are used to calculate vapor-phase compositions. The activity coefficients of the solution were correlated with the Wilson, NRTL, Margules, van Laar, and UNIQUAC models through the fit of the least-squares method. The VLE data of the ternary system were well-predicted from these binary interaction parameters of Wilson, NRTL, Margules, van Laar, and UNIQUAC model parameters without any additional adjustment to build the thermodynamic model of VLE for the ternary system and obtain the vapor-phase compositions and the calculated bubble points. The calculated bubble points with the model parameters of activity coefficients were in good agreement with the experimental data.