Abstract: The removal of NO by viscose base activated carbon fibers were carried out on a fixed-bed adsorption reactor. The methods such as hydrogen peroxide (H₂O₂) solution impregnation, heat treatment were employed separately to modify the activated carbon fibers. The NO removal efficiency was investigated using the activated carbon fibers before and after modification in the inert nitrogen atmosphere, oxygen-containing atmosphere. Furthermore, the change of activated carbon fibers characteristics, such as pore structure as well as nitrogenous or oxygenous surface functional groups, was also discussed in order to explore the effect of oxygen-containing functional groups and O₂ in atmosphere on the NO catalytic oxidation and the transformation process of NO to NO₂. The results show that in the nitrogen atmosphere the C-O functional groups of the activated carbon fiber surface can oxidize the adsorbed NO to be -NO₂. On the other hand, in the oxygen atmosphere -NO₂ and -NO₃ are detected in the activated carbon fibers surface after the NO adsorbing. It is found that NO removal efficiency in stable stage after long time test is almost the same for the original activated carbon fibers as well as the two modified ones, which indicates that the transformation of NO to NO₂ is mainly resulted from the reaction between the adsorbed NO on activated carbon fibers and the free oxygen in atmosphere.