Experimental and numerical work was performed for the laminar film condensation of steam-air mixture flow over a flat plate. For small temperature difference between the gas mixture and the cold wall, the gas mixture in the boundary layer can be treated as superheated gas. When the temperature difference is large, the gas mixture becomes supersaturated near the interface. In that case, mist formed near the interface, the temperature profile of the gas mixture was greatly concaved toward the interface and the heat transfer was enhanced. However the velocity profile measured by the laser Doppler anemometer (LDA) showed the same trend without mist formation. A calculation model is proposed and compared with the experimental data and previous models for the superheated or the saturated conditions.