Excess molar enthalpies for the ternary mixture n-propanol + acetic acid + n-propyl acetate were measured with the C80 calorimeter (Setaram) equipped with membrane mixing cells at 313.15 K and atmospheric pressure. Different degree polynomials were used to correlate the experimental data. Redlich–Kister equation for multicomponent systems showed the best result. A smooth representation of the results was used to construct constant-enthalpy contours on a Roozeboom diagram. The system showed mostly endothermic character at the measured temperature. The capability of the NRTL model to predict these data was also studied. It was established that the NRTL model enabled to predict excess molar enthalpies using the interaction parameters of constituent binary sub-systems with an error 10–20 %.