In this paper, sludge activated carbon was made from two kinds of sludge by physical-chemical methods. The sludge was taken from the Gaobeidian municipal wastewater treatment plant in Beijing and ZnCl(2) was used as activated reagent. The adsorption mechanism of gatifloxacin, a new 4-quinolones antibiotic, by the two kinds of sludge activated carbon was studied. The Characteristics of sludge and sludge activated carbon, such as specific surface area, zeta-potential, particle size distribution, stereoscan photograph, were tested in order to have a better understanding about the adsorption mechanism. The results show that the sludge activated carbon can adsorb antibiotic effectively. The sludge activated carbon made of the sludge from sedimentation tank has a better adsorption capability than that from dewatering house. Meanwhile, the adsorption can be affected by environmental conditions. Higher temperature can enhance the adsorption. Moreover, a lower CaCl(2) concentration can restrain the adsorption, while a higher concentration can promote it. This study shows that it is applicable for sludge activated carbon to be used as an adsorbent to treat antibiotic wastewater or nondegradable wastewater. It also shows a new direction for sludge disposal and sludge reuse as a resource.