Isothermal vapor-liquid equilibrium data of the binary system pentafluoroethane (HFC-125) + propane (R-290) were measured in the temperature range from 273.15 K to 313.15 K at 10 K intervals and in the composition range from 0.1 to 0.8 mole fraction HFC-125. Temperature, pressure, and compositions of the liquid and vapor phases were measured with a circulation-type apparatus. The experimental data were correlated with the Carnahan-Starling-De Santis, Peng-Robinson, and Redlieli-Kwong-Soave equations of state. Azeotropic behavior was revealed near 0.77 mole fraction HFC-125. The vapor pressure of the azeotropic system is between those of chlorodifluoromethane (HCFC-22) and the zeotropic mixture of difluoroethane (HFC-32) + HFC-125 (50-50). This azeotropic system hasu good potential to replace the use of HCFC-22 as a refrigerant.