The effects of nitrogen-doping on adsorption properties of activated carbon fibers (ACFs) for NO were investigated. The nitrogen-doped ACFs (N-ACFs) were prepared by chemical vapor deposition (CVD) of pyridine at 1023 K for various times. The N-ACFs were characterized by N-2 adsorption at 77 K, elemental analysis, and X-ray photoelectron spectroscopy (XPS). The nitrogen content increases with the pyridine-CVD time. An XPS examination showed that the fraction of quaternary nitrogen in the nitrogen structures is almost constant, regardless of the CVD times. However, quaternary nitrogen increases remarkably from 54% to 78% after heat-treatment of N-ACF at 1273 K, although the total nitrogen content decreases. The adsorption properties of N-ACFs for NO were examined at 303 K. The NO adsorption capacity of N-ACFs increases with the concentration of doped nitrogen. The NO adsorptivity of the N-ACF was remarkably enhanced by the heat-treatment at 1273 K.