Abstract: Condensation heat transfer of vapor-gas mixture in turbulent downflow through a vertical annulus has been studied. An analytical model, relatively simple in computation, is developed using available correlations for the interfacial shear stress, heat and mass transfer coefficients. The solutions obtained for steam-air mixtures agree well with experimental data of Stewart et al. and Kasprzak and Podpora. The effects of main stream Reynolds number and radius ratio r* are found to be significant for flow condensation of mixtures in annuli.