Vapor-liquid interfacial tensions of miscible mixtures have been predicted by applying the gradient theory to an improved Peng-Robinson equation of state. The modified Huron-Vidal mixing rule model has been considered for fitting vapor-liquid equilibrium data of miscible polar and non-polar mixtures and, then, for predicting the interfacial tension of these mixtures. According to results, an accurate and globally stable fitting of the vapor-liquid equilibrium data results on a physically coherent prediction of interfacial tensions in the full concentration range. In addition. we present a criteria based on the geometry of the grand potential function along the interface for assessing the predictive value of the GT. Calculations for subcritical binary mixtures are presented and compared to experimental data and the Parachor method for demonstrating the potential of the unified approach suggested in this work. (C) 2004 Elsevier B.V. All rights reserved.