PURPOSE: To provide a method for removing nitrogen oxide by which nitrogen oxide of low concentration included in a gas is effectively adsorbed and removed to adsorb and remove nitrogen oxide in the air.

CONSTITUTION: Gas contg. nitrogen oxide of low concentration of ≤50ppm is brought into contact with activated carbon fiber to adsorb the nitrogen oxide. The adsorbed nitrogen oxide is heated in an inert gas to desorb the nitrogen oxide to obtain a gas contg. concentrated nitrogen oxide. Next, the gas contg. concentrated nitrogen oxide is treated by denitrification equipment to remove the nitrogen oxide. As the activated carbon fiber, that of 3-15μm fiber diameter and 200-1000m2/g specific surface area is suitable.