This paper reports on the permeability of alumina membranes with pore diameters of a few nanometers for pure liquids. It appears that the volume flux corrected for viscosity differences depends on the type of permeant. It decreases in the order water, hexane, ethanol, s-butanol. The hydraulic resistance defined as the reciprocal permeability) of supported membranes can be taken as the sum of the hydraulic resistance of the membrane and that of the support. This implies that the membrane material does not penetrate the pores of the support significantly. The Kozeny—Carman constant for alumina membranes calcined at 800°C amounts to 13.3±2. This value is much higher than the commonly found value of 5. This can be explained by taking into account the plate shape of the crystallites forming the membrane, resulting in a microstructure with a high value for the tortuosity.