This paper deals with the theoretical analysis of laminar forced convection condensation of binary mixtures on a flat plate. Similarity solutions for seven kinds of binary mixtures of ethanol-water, R 22-R 114, R 114-R 11, air-water, air-ethanol, air-R 22, air-114 along with several pseudo-mixtures of low Shmidt number and low ρ-μ ratio are numerically obtained. Two expressions among the boundary values at the vapour-liquid interface concerning heat and mass flaxes through the vapour boundary layer are newly proposed, which contain the characteristics of condensation of superheated and saturated pure vapours and those of single phase forced convection. The heat and mass fluxes calculated from the simultaneous algebraic equations which are composed of the present new expressions, previous expression for liquid film heat transfer, phase equilibrium conditions and miscible condition, agree with those from the similarity solutions within 1-3% error.