An experimental study of gravity controlled condensation of binary vapor mixtures of methanol-water, ethanol-water and methanol-ethanol on a smooth horizontal tube was carried out. The condensation of methanol-water mixtures is dropwise in the range y_lGb=0.08-0.85. For ethanol-water mixtures there are four condensation patterns observed: the pattern in the range y_lGb=O.28-0.60 is dropwise, while that in the range Y_lGb=0.73-0.83 changes from streak to filmwise through ringwise as the heat flux density increases and that near azeotrope is filmwise. For methanol-ethanol mixtures the pattern is filmwise. Heat transfer coefficient of the condensate was calculated under the assumption that mass transfer in the vapor layer could be estimated by the present authors' theory for laminar filmwise condensation based on the two phase boundary layer concept. The results for non-filmwise condensation are 2 to 6 times higher than the theoretical values, while those for filmwise condensation are fairly in good agreement.