The preparation of nitrogen-rich activated carbon can be achieved by the use of nitrogen-rich precursor or by the nitrogenous modification for carbon surface. In this study, the activated carbon fiber (ACF) was prepared from polyacrylonitrile (PAN) containing ca. 25 wt% nitrogen as a precursor. The prepared PAN-ACF was further treated by urea as a nitrogen medium to introduce the nitrogen functional groups after air oxidation treatment. The surface analysis of urea-treated PAN-ACF by X-ray photoelectron spectroscopy (XPS) revealed that the amount of negatively charged nitrogen species was relatively high compared to PAN-ACF. The result of Cd(II) adsorption experiment indicated that the amount of Cd(II) adsorption was increased in the order of commercial ACFs, PAN-ACF and urea-treated PAN-ACF. The examination of the effect of coexistence between Cd(II) and aromatic compound indicated that Cd(II) adsorbed on p electron clouds of the nitrogen-poor ACF, while not only p electron clouds but also newly introduced specific basic nitrogen/oxygen functional groups contributed to Cd(II) adsorption. These specific sites would not be affected by aromatic compounds.