We prepared alumina tubes by an anodic oxidation process. The tube obtained was mechanically tough against a pressure of about 1 MPa from the outside of the tu be. The tu be was characterized by scanning electron microscopy (SEM) and a gas permeability measurement. The SEM observations revealed that this has uniform straight channels penetrating through the tube wall. The channels are vertical to the tube surface and their dia meter is a bo ut 150 nm. The permeability of gas was measured with H-2, He, N-2, O-2 and CO2 in the range of 0-100 kPa. The gas flow was mainly governed by Knudsen flow. This indicates the absence of big cracks in the tube.