The speed of sound in the liquid phase for binary mixtures of pentafluoroethane (CHF2CF3) and 1,1-difluoroethane (CHF2CH3) was measured along six isotherms from (243 to 333) K and at pressures from near the saturation line up to about 30 MPa. The measurements were carried out by a sing-around technique operated at a frequency of 2 MHz employing the fixed-path acoustic interferometer. The combined uncertainty is estimated to be within 0.2% in the high-density region. The speed of sound in the saturated liquid was estimated by an extrapolation of data obtained for the compressed liquid to the vapor pressure. The results for (1 - x)CHF2CF3 + xCHF(2)CH(3) measured for mole fractions x = 0.3806, 0.6445, and 0.8447 were correlated by the polynomial equation as functions of temperature and pressure. The variations in the speed of sound with the composition at various temperatures and pressures are discussed for the system investigated as well as for (1 - x)CHF2CH3 + xCF(3)CH(2)F and (1 - x)CHF2CH3 + xCF(3)CH(3) reported elsewhere.