We were chosen Seongnam sludge with the highest ratio of A1₂O₃/SiO₂(0.912) and Sukseong sludge with the lowest ratio of Al₂O₃/SiO₂(0.345) out of various sludges. It has been investigated the relationship between Al₂O₃/SiO₂ and its adsorption capability, then make criteria to choose the optimum sludge for final applications. The adsorption properties of heat-treated sludges were determined with the following parameters; three types of heavy metal ions(Cd⁺³, Cr⁺⁶, Pb⁺³), the concentration, adsorption period and pH of the solutions.