Based on the absolute-rate theory and the two-liquid solution theory, a new equation is proposed to predict the dependence of the binary mutual diffusivities on concentration. The equation, in terms of the diffusion coefficient at infinite dilution, the correction factor for thermodynamic nonideality, and the acentric factor, predicts the behavior of the diffusion coefficient generally well. Further, another new equation, in which only the diffusion coefficient at infinite dilution and some basic properties (acentric factor, critical pressure, molecular weight, and dipole moment) are needed, is proposed and tested to predict the mutual liquid diffusion coefficients for 38 different binary systems. The results of prediction shows that this new equation is more successful than either Vignes’ equation or Asfour-Dullien’s equation in predicting the concentration dependence of the diffusion coefficients as a whole, though it-does not require a correction factor for thermodynamic nonideality or viscosity data.