Abstract Li M.-H. and Wang Y.-L., 1992. Application of approximations to mixture radial distribution functions to the development of mixing rules. Fluid Phase Equilibria, 72: 89-110. The mixing rules utilizing the approximations for mixture radial distribution functions have been presented for extension of an equation of state of polar fluids to mixtures. The van der Waals one-fluid approximation and the mean density approximation (MDA) for radial distribution functions in a mixture have been applied to derive mixing rule models. To investigate further the composition dependence of the MDA, the composition-dependent cross-interaction energy parameter is also introduced; the resulting model is referred to as the modified mean density approximation (MMDA). In calculations of the vapor-liquid equilibria for non-ideal fluid mixtures, satisfactory results were obtained by the MMDA. When performing the vapor-liquid equilibrium calculations for systems with data over a wide range of temperatures, the MMDA also yielded reasonable results. Furthermore, the proposed method can be used to extend any existing accurate corresponding-states-type pure-fluid equation of state to mixtures.