Effects of Al stress on membrane lipid peroxidation and antioxidant enzyme activities of black soybean for acid-resistant type (Glycine max Tamba,referred to RB) and acid-sensitive type (referred to SB) were investigated under hydroponic conditions in this study.The results showed that RB was more resistant to Al stress than that of SB.H₂O₂ and malondialdehyde contents in SB leaves and roots were elevated more obviously than those in RB leaves and roots under Al stress,indicating that membrane lipid peroxidation in SB was greater than that in RB.Enzyme activity measurement suggested no significant difference was observed in leaf and root SOD activity between RB and SB under Al stress.However,leaf and root CAT activity were all induced and elevated markedly after RB and SB were treated with different concentration of Al.Moreover,leaf and root POD activity in RB displayed a descending trend but were still higher significantly than those in SB under Al stress.As compared with SB,RB possesses a stronger antioxidant enzyme system which confers on it a higher ability to scavenge ROS under Al stress.Thus,Al-induced lipid peroxidation was weaker in RB than that in SB.The data suggested that antioxidant enzyme system plays an important role in the Al-resistance mechanism of RB.