In this study,the Al-sensitive black soybean (SB) was taken as experimental materials under Al stress to investigate the physiological and molecular mechanisms of the effect of the pretreatment with hydrogen peroxide (H₂O₂) on alleviating aluminum toxicity.The results show that:(1)The relative root growth of SB is promoted significantly with 0.1 and 1.0 μmol·L^-1 H₂O₂ pretreatment,but promoted first then inhibited with 10.0 and 100.0 μmol·L^-1 H₂O₂ pretreatment.(2)Exposure to different Al concentrations (50～400 μmol·L^-1) 3 weeks after pretreatment with 1.0 μmol·L^-1 H₂O₂,the total protein content was increased in both leaves and roots by 16.7%～41.2% and 10.0%～25.0%,respectively;the MDA content was significantly decreased by almost 50%;the activities of SOD and POD improved greatly in SB.(3)RT-PCR analysis showed that pretreatment with H₂O₂ also increased the expression level of SOD both in SB root and leaf under Al stress.Taken together,pretreatment with H₂O₂ can promote the growth of SB greatly and enhance the capacity to Al stress by the means of increasing the activities of antioxidant enzymes and their expression levels.