Experiments on ternary distillation were made for a nitrogen-argon-oxygen system in a wetted-wall column under total reflux conditions for wide ranges of vapor concentrations and flow rates (especially turbulent flow region), and simultaneous heat and mass transfer was examined. Heights of transfer units for the intermediate component, argon, show discontinuity near the zero driving force region. The observed diffusion fluxes of each component in ternary distillation are found to be proportional to their concentration driving forces, whereas the observed mass fluxes are not. This is due to the convective mass fluxes caused by mass fluxes of the other components. The observed diffusion fluxes in the ternary distillation of air show good agreement with the previously developed binary correlation using Wilke＇s effective diffusion coefficients. The separation performance of cryogenic air distillation under total reflux conditions in a wetted-wall column is predicted by using the correlation for ternary diffusion fluxes, Predicted separation performance shows good agreement with the observed data. The effect of interaction between diffusion fluxes in air distillation is also discussed.