Tert-butyl alcohol(TBA) and isopropyl alcohol(IPA) which showed an azeotrope with water at atmospheric pressure were dehydrated in a wetted-wall column by the diffusion distillation. The diffusion distillation process was made up of wetted-wall column which consists of two concentric tubes and an inert gas layer. The liquid mixture introduced at the top of column flowed down and evaporated below the boiling temperature and diffused through an inert gas layer with different diffusion rate and then condensed at the plate which kept at low temperature. Experiments were carried out at various evaporation side temperatures, and with various kinds of gases such as CO₂, air and helium. The diffusion length was varied by interchanging of inner tubes of different diameters. The degree of separation was presented by selectivity and flux of condensed side. The selectivity was defined as the difference in composition between the evaporation and the condensation side. TBA/water and IPA/water systems were found to show the maximum selectivity at 35℃ and 40℃, respectively. With increasing evaporation side temperature, the flux was increased. The highest selectivity was obtained with carbon dioxide as an inert gas and the highest flux with helium. The selectivity and the flux were increased with decreasing the diffusion length. The experimental data were compared with the theoretical results.