Extractable noncrystalline aluminum in red soils could be fractionated into exchangeable Al (ExAl), adsorbed inorganic hydroxy-Al (HyAl), organic complexed Al(OrAl), Fe oxide bound Al (DCBAl), interlayered Al (InAl) and noncrystalline aluminosilicate (NcAl), by the 1 mol/L KCl, 0.2mol/L HCl, 0.1 mol/L Na₄P₂O₇ (pH8.5), DCB solution, sodium citrate (0.33 mol/L, pH7.3) and 0.5 mol/L NaOH sequential extraction. All Al forms were characterized by the intrinsic feature in their composition and properties and closely related to the corresponding properties and ecological characteristics of red soils. In the same soil sample the amounts of various Al forms were of the order NcAl>InAl>DCBAl>OrAl>HyAl>ExAl. With the exception of ExAl content the contents of other five forms of aluminum in the red soils derived from basalt were higher than those from granite. In soils most of the aluminum existed in layer aluminosilicate minerals. Individual extraction of the Al forms in soils was compared with the sequential extraction method.