Biomass adsorbent which is a kind of activated carbon was successfully prepared from biomass. The watermelon-seed was used as a raw material for the production of activated carbon. Preparation process involves the roasting of raw material and carbonization of roasted material followed by chemical activation. Chemical activation was carried out by using phosphoric acid as an activation agent at 700℃, 2hr. N2-BET surface areas of activated watermelon char prepared by chemical activation were measured as about 283~968m2/g. The adsorbate transmittance of copper(II) was determined UV absorption at 740nm as maximum absorption wavelength using UV spectrophotometer. Removal of copper(II) in solution by activated carbon was carried out and structural change of pore surface was observed by SEM.