Both theoretical and experimental studies were made on the rate of sodium vapor deposition onto a horizontal flat plate above hot liquid sodium surface. The conditions for the generation of sodium mist within cover gas were also investigated. The similarity of heat and mass transfer was used in theoretical analysis. Basic equations for the formation of sodium mist, temperature distribution, and the amount of sodium deposition onto the flat plate are derived and presented together with the explanation of some assumptions. Analytical results about the conditions for the generation of sodium mists and about the rate of sodium vapor deposition are presented by figures with the sodium temperature as an parameter. An experiment was also made to examine the relation between the sodium vapor deposition rate and the temperatures of sodium and plate surfaces. Experimental method and the results of measurements are presented. Finally, some conclusions are drawn from those theoretical and experimental analysis. It is deduced that the sodium mist in the cover gas grows around a small particle having a radius of 10/sup -6/ - 10/sup -7/ cm.