Abstract: An equation for predicting the surface tensions of binary liquid mixtures from the properties of the bulk liquids and surface tensions of the pure substance has been established on the basis of Gibbs-Duhem's equati0n along with the contribution of two simple surface models. It gave satisfactory results for running 216 binary mixtures. For more than a half of these systems, the standard deviations of the predicted surface tensions are less than 0.0005N/m and about three-quarters are less than 0.001 N/m without using any binary informations and any adjustable parameters. However, for the surface tensions of aqueous systems and some strongly associated binary mixtures a little higher deviations between the experimental values and the predicted ones have been found. This equation appears to provide a sound basis for establishing a more reliable model for predicting the surface tensions of the multicomponent mixtures too.