Utilizing porous polyacrylonitrile (PAN) fibers as the precursors, porous carbon fibers were obtained by cross-linking of precursor fibers with hydrazine hydrate and subsequent heat treatment. A nitrogen content of more than 14 wt % was achieved in the carbon fibers. The porous carbon fiber that was prepared at low concentration of hydrazine hydrate (5 wt %) showed an optimal BET surface area of 277.4 m(2)/g with micro-/meso-/macropores. The CO2 adsorbed amount of this porous carbon fiber was 101 mg/g at 25 degrees C under atmospheric pressure, which was 2.1 times that of the fiber without cross-linking with hydrazine hydrate. In the simulated flue gas environment (10% CO2/90% N-2), the adsorption capacity of the above-mentioned porous fiber was 32 mg/g at 25 degrees C, which was 1.4 times that of the fiber without cross-linking. These CO2 adsorption results demonstrated that the nitrogen functionalities and porous structure of the porous carbon fiber played an equivalent important role in the adsorption of CO2. The porous carbon fiber also owned an excellent CO2 reusability, and 96% of the adsorption capacity was maintained after 20 cycles of CO2 adsorption and desorption. The porous carbon fibers enriched with nitrogen could thus be a potential material for CO2 capture.