A novel process was developed to induce a simultaneous oxidation of ammonia and denitrification in a single system consisting of two chambers separated by a cation exchange membrane. One was an anoxic chamber and the other was an aerobic chamber. The maximum mass flux via the membrane was calculated as 0.83mg NH 4 + -N/m 2 s in a batch test when the initial concentration of NH 4 + was 700mgN/L. And it was observed that NO 3 − and NO 2 − moved via the membrane in a reverse direction when NH 4 + was transported. When the system was operated in a continuous mode by feeding a wastewater containing glucose and NH 4 + , it was observed that soluble chemical oxygen demand and NH 4 + were simultaneously removed showing 99% and 71∼86% of efficiency, respectively. Denitrification occurred in the anoxic chamber and nitrification was carried out in the aerobic chamber.