Surface tensions of binary mixtures of dimethylsulfoxide (DMSO) + water, diethylsulfoxide (DESO) + water, dipropylsulfoxide (DPSO) + water, and diisopropylsulfoxide (DiPSO) + water have been determined at (298.15, 303.15, 308.15, 313.15, 318.15, 323.15, and 328.15) K. The refractive index for the above-mentioned systems has been measured at (298.15, 303.15, and 308.15) K. An unusual behavior of the concentration dependence of surface tension observed for the DMSO + water system is explained on the basis of changing intermolecular interactions involving DMSO self-association and DMSO association with water.