Electrochemical separation of oxygen from air using an anion exchange membrane is investigated. When oxygen contained gas is supplied to the cathode at the ambient temperature and pressure, hydroxide ion will be formed reacting with water and migrates to the anode to produce pure oxygen. We confirmed the hydroxide ion selectivity of the membrane through membrane potential measurement and electrolysis experiments. Oxygen is produced at electrochemically equivalent rate at the anode. Rate determining steps are charge transfer for both formation and decomposition of hydroxide ion. But about 2.0 V is required for 1000 A.m(-2) current density. Adding alkali to the cathode decreased the cell resistance significantly.