As one of the promising alternative refrigerants to replace R-502 [R-22 + R-115 (XR-22 = 0.63, where x denotes mole fraction)], the gas-phase thermodynamic properties of the ternary mixture R-32 (difluoromethane) (1) + R-125 (pentafluoroethane) (2) + R-143a (1,1,1-trifluoroethane) (3) have been studied. A total of 220 gas-phase PVTx properties for the present ternary system, R-32 + R-125 + R-143a, was obtained at four different compositions, (x(1) = 0.174, x(2) = 0.340), (x(1) = 0.313, x(2) = 0.203), (x(1) = 0.343, x(2) = 0.445), and (x(1) = 0.484, x(2) = 0.216), by using the Burnett apparatus. The present measurements range widely in temperature (305 to 380) K, pressure up to 4.6 MPa, and density up to 200 kg(.)m(-3). The uncertainties of the present study are estimated to be within 7 mK in temperature, (0.8 to 2.5) kPa in pressure, 0.15% in density, and 0.1 mol % in composition. The second and third virial coefficients for the mixtures, B-m and C-m, were also obtained from the present isothermal PVTx data. The consistency of the present measurements was confirmed by comparing them with the virial equation of state for the mixture of interest developed by the present authors and REFPROP. An excellent agreement between the present measurements and those models was confirmed to be within +/-0.4% for pressure and +/-0.1% for the mixture second virial coefficients.