Abstract: The sol charged positive of magnesium aluminum double hydroxide （MADH） was prepared by using AlCl₃·6H₂O, MgCl₃·6H₂O and NH₃·H₂O as raw materials. The behavior of MADH in decolorization process was studied using simulated wastewater containing different kinds of soluble dyestuffs, and the mechanism of decolorization was discussed. The results showed that the efficiency of decolorization was obviously high for the anionic dyestuff, such as reactive, acidic or direct dye, at the optimum pH range 6～9 and the optimum reactive time 10 min. The decolorization rate reached above 99% if enough dose of MADH was added. The maximum absorbable quantity, i.e. absorbed anionic dyestuff per unit MADH, was 327～2 113 mg/g. Higher temperature was unfavorable for absorption process. In practical treatment of textile effluent by MADH, the decolorization and COD Cr removal were also effective. The mechanism of decolorization was chemical absorption of MADH on dyestuff. Also, the decolorization effect for cationic dyestuffs was not desirable.