Batch and column adsorption of divalent cadmium ions from aqueous solution using oxidized activated carbon (OAC) was investigated. Commercially available bead-shaped activated carbon (BAC) was oxidized with ammonium persulfate, and Cd(II) adsorption experiments were performed in batch and flow systems. The total amount of Cd(II) adsorbed in the flow system was 1.7 mmol/g, which was asymptotically equal to the maximum amount adsorbed in the batch system. Regeneration of the adsorbent was evaluated via Cd(II) desorption from OAC using 0.1 M nitric acid. The total Cd(II) desorbed was approximately 1.9 mmol/g, which was nearly equivalent to the total Cd(II) adsorbed in the flow system. The amount of Cd(II) adsorbed using regenerated OAC in the 2nd-cycle was not significantly different from that adsorbed in the 1st-cycle. These results imply that OAC is prospectively reusable for Cd(II) adsorption applications.