The wave structure of condensate film and the characteristics of boundary layer flow in the vapor phase were investigated experimentally for condensation of steam-air mixture on a vertical surface. The instantaneous film thickness and the fluctuating temperature in the boundary layer were measured simultaneously. Also the heat transfer coefficient across the condensate film and the diffusion layer formed by air (noncondensable gas) was obtained at various film Reynolds numbers and vapor velocities. The influence of the wavy interface on the temperature field and the heat transfer depend strongly on film Reynolds number and vapor velocity. The condensation heat transfer coefficient increases more than several tens percents with the increase of film Reynolds number depending on the vapor velocity. The fluctuating temperature correlates strongly with the waviness of condensate film corresponding to film Reynolds number. The RMS (root-mean-square) of the temperature fluctuation increases considerably due to the waviness and shows a maximum value around the crest of large amplitude waves.