Abstract: With the method of sequential extraction,the extractable noncrystalline aluminum in Acid Sulfate Soils was fractionized into exchangeable Al (ExAl),absorbed inorganic hydroxy-Al(HyAl),organic complexed Al(OrAl),Fe oxide bound Al (DCBAl),interlayered Al(InAl) and noncrystalline aluminosilicate(NcAl) with average of 1.79,2.51,4.17,4.14, 4.31 and 8.66gAl₂O₃.kg^-1,respectively.In actual Acid Sulfate Soils, the amount of different forms Al followed the order of NcAl>OrAl>InAl>DCBAl>ExAl>HyAl, but in potential acid sulfate soils, NcAl>InAl>DCBAl> HyAl>OrAl>ExAl. The average of the total extractable noncrystalline Al was 35.57 g Al₂O₃.kg^-1,which covered 25.04 % of the total amount of Al in Acid Sulfate Soils. The characteristic of extractable noncrystalline Al in Acid Sulfate Soils was the high proportion of active aluminum, such as ExAl,HyAl and OrAl. All forms of Al were closely related to the corresponding properties and ecological characteristics of Acid Sulfate Soils. The strong acid environment of actual Acid Sulfate Soils induced over released Al, which transformed to active Al and resulted in Al toxicity.