An anodic aluminum oxide tube with perforated straight pores to use as a porous membrane or as a support for a composite membrane was prepared. An aluminum oxide layer with straight micropores dosed by an oxide barrier layer was formed on the surface of an aluminum tube, 45 mm long, 0.5 mm thick and 6 mm in outer diameter, by anodic oxidation in an aqueous solution of oxalic acid. The pores were opened by dissolution of the inner aluminum and the subsequent barrier layer of aluminum oxide. The tubular alumina membrane obtained was 35-40 mu m thick with straight micropores of 20-50 nm, and therefore showed Knudsen permselectivity for inorganic gases. It was found that the tube could withstand at least up to 4.4 atm of transmembrane pressure.