A series of activated carbon was prepared from biomass by chemical activation with ZnCL₂, NaOH and KOH. The seed of water-melon was used as raw materials. Preparation process involves the roasting of raw material and carbonization of roasted material followed by chemical activation. The final product was washed throughly with hot water and finally dried at 110 ℃. N₂-Langmuir surface areas of activated water-melon char prepared by chemical activation were measured as 72 ~ 978 m²/g, respectively. Removal of chromium in solution by activated carbon was carried out and structural change of pore surface was observed by SEM.