The vapor-liquid equilibria (P-T-x-y) data of the binary mixture of dimethyl ether and propyl acetate (n-propyl acetate) were obtained by two procedures. First, binary mixtures of dimethyl ether + propyl acetate in various proportions were loaded into vapor-liquid equilibrium cells with an inside volume of 1.56 x 10(2) cm(3), and the pressure and temperature were measured using the static method after it reached thermodynamic equilibrium. The operating temperature and pressure range from 253.2 K (-20 degreesC) to 443.2 K (170 degreesC) and from 100 kPa to 4000 kPa, respectively. Second, the pressure, the mole fractions and volumes of the vapor phase and the liquid phase, were calculated with two equations of state, the Peng-Robinson equation of state and Soave-Redlich-Kwong equation of state, assuming that the binary interaction parameter, k(ij), was zero. Finally, the optimum binary interaction parameters for these two equations of state were determined as a function of temperature by minimizing the difference between calculated pressure and experimental data.