Vapor-liquid-liquid equilibria (VLLE), azeotropic, and excess enthalpy (HE) data for the binary system n-undecane + propionamide were measured at temperatures from 359.25 to 416.65 K. Additionally, pure-component vapor pressure and density data for propionamide were determined experimentally. The LLE and VLLE measurements were performed in a stirred glass cell and in a static equilibrium cell with a capability to take small samples from the different phases by using pneumatic micro samplers. For the HE measurements, an isothermal flow calorimeter was used, and the azeotropic data were obtained from distillation experiments using a micro spinning band column. The pure-component vapor pressures and densities were measured with the help of the dynamic method (ebulliometer) and a vibrating tube densimeter, respectively. To the experimental mixture data from this work linear temperature-dependent interaction parameters for the NRTL model were fitted. They can be used to represent the phase equilibrium behavior and excess enthalpies of the investigated system.