The surface tensions of the binary mixtures 1,1,1-trifluoroethane (R-143a) + 1,1,1,2-tetrafluoroethane (R-134a) were measured in the temperature range from (257 to 329) K using the differential capillary rise method under vapor-liquid equilibrium conditions. The uncertainties of measurements for the temperature and surface tension were estimated to be within +/-10 mK and +/-0.15 mN(.)m(-1), respectively. The experimental surface tension data of R-143a + R134a were correlated as a function of the mass fraction using the correlations for pure R-143a and R-134a.