NOVELTY - Polyvinyl alcohol is added to sodium carboxymethyl cellulose or sodium alginate aqueous solution. Dispersed carbon nanotubes are added and stirred to obtain a thick membrane solution. The membrane solution is cast, dried, soaked in ferric chloride solution, crosslinked, washed, and dried to obtain a cationic exchange membrane. An anionic membrane solution is prepared by stirring glutaraldehye with chitosan acetate solution. The solution is cast and fixed with the cationic exchange membrane, and dried to obtain a bipolar membrane.    USE - Preparation of bipolar membrane modified with carbon nanotube with anionic group.    ADVANTAGE - The method provides bipolar membranes having excellent water-dissociation efficiency, low membrane resistance, low cell voltage, and excellent compatibility with respect to the two membrane layers.    DETAILED DESCRIPTION - Sodium carboxymethyl cellulose or sodium alginate is weighed and prepared into 1-10 %mass aqueous solution. Polyvinyl alcohol is added to and dissolved in the aqueous solution. Carbon nanotubes with anionic group are weighed, added to ethanol, ultrasonically vibrated, and uniformly dispersed. The dispersed nanotubes are added to the aqueous solution, stirred, and vacuum-debubbled to obtain a thick membrane solution. The membrane solution is cast on a flat vessel, dried at room temperature to form a membrane, soaked in 1-10 %mass ferric chloride solution, crosslinked for 10-30 minutes, washed with distilled water, and naturally dried to obtain a polyvinyl alcohol-carboxymethyl cellulose-nanotube cationic exchange membrane or sodium alginate-carboxymethyl cellulose-nanotube cationic exchange membrane. Chitosan is mixed with 1-10 %mass acetic acid solution to obtain 1-10 %mass chitosan acetate solution. 2.5 Vol.% glutaraldehyde is slowly dripped and stirred and vacuum-debubbled to obtain anionic membrane solution. The anionic membrane solution is cast into a membrane, laminated, bound or hot-pressed and fixed with the cationic exchange membrane, and dried at room temperature to obtain a polyvinyl alcohol or sodium alginate-carboxymethyl cellulose-nanotube/chitosan bipolar membrane.