Sludge tends to accumulate easily in lake due to the closed water system and the pollutants contained inside could cause serious environmental problems. The sludge accumulation is mainly solved by dredging the lake, although the general disposal method of the dredged sludge by landfilling remains a problem due to formation of soft-ground and limited space. In this study, the conversion of the dredged sludge into adsorbent material that can be used for water treatment was tried. Using hydrothermal treatment in alkali medium, lake sludge which main components are silica and alumina could be converted into zeolite. The effects of various treatment conditions (NaOH concentration, alkali solution volume to dry sludge weight L/S ratio, Si/Al molar ratio, reaction temperature) were investigated. The adsorption abilities of synthesized zeolites were evaluated by measuring the cation exchange capacity (CEC) value and adsorption capacity towards heavy metals in aqueous solution (Pb, Cd). Soluble elements in sludge such as silica and alumina tend to dissolve at higher temperature and form zeolite. Zeolite type Na-P1 which was synthesized at silica/alumina (Si/Al) ratio of 2.5 and reaction temperature of 120°C showed the highest CEC value. The synthesized zeolites showed some adsorption ability towards heavy metals in aqueous solution (Pb2+ (Xm=55.3mg/g) and Cd2+ (Xm=40.9mg/g)).