Activated carbons (ACs) were prepared from sulfur-containing petroleum coke (PC, sulfur content 8%) and oxidized to introduce sulfo groups. The effect of specific surface area of ACs on the amount of Ni(II) adsorbed on oxidized ACs was examined. PC was first activated with potassium hydroxide (KOH) at a KOH/PC mass ratio of 1-3, an activation temperature of 400-850 degrees C, and an activation time of 0.5-2.0 h. The specific surface area and total pore volume of the ACs prepared were 510-1,890 m(2)/g and 0.25-1.07 cm(3)/g, respectively. In the second step, ACs were oxidized with concentrated nitric acid under the same conditions, and Ni(II) adsorption from water onto oxidized ACs was compared with that onto oxidized commercial bead shaped activated carbon (BAC, sulfur content less than 0.02%). The results showed that Ni(II) adsorption onto oxidized ACs increased linearly with the increase in specific surface area of ACs from 500 to 1,000 m(2)/g and reached saturation at 3.5 mmol/g in the range of 1,000-1,900 m(2)/g. Oxidized ACs adsorbed Ni(II) even at low solution pH of 1.0, whereas no adsorption onto oxidized BAC was observed, suggesting that sulfo groups were present on the surface of oxidized AC prepared from sulfur-containing PC.