Isothermal vapor-liquid equilibrium data for the binary mixture of 1, 1, 1,2,3,3,3-heptafluoropropane (HFC227ea) + butane (R600) were measured at (273.15, 283.15, 293.15, 303.15, 313.15, and 323.15) K, respectively. The experiments were carried out using a continuous circulation-type equilibrium apparatus to measure temperature, pressure, and the compositions of the liquid and vapor phases. The experimental data were correlated with the Peng-Robinson equation of state (PR EOS) using the Wong-Sandler mixing rule. Calculated results showed good agreement with experimental data. It was found that this system has,very strong positive azeotropes for all the temperature ranges studied here.