In this study,the Tamba Black soybean (RB) was used as the experimental material to analysis the physiological mechanism of exogenous IAA increasing Al resistance by investigation the effect of exogenous IAA on the contents of endogenous IAA,H₂O₂,MDA,Al,citrate exudation and the activities of the plasma membrane (PM) H⁺-ATPase under Al stress.The results showed that after exposure to 25,50 and 200 μmol·L^-1 AlCl₃ for 24 h,the contents of endogenous IAA,citrate exudation and the activities of the PM H⁺-ATPase in RB roots were firstly promoted,then decreased.However,the contents of H₂O₂ and MDA were increased significantly with Al concentrations increasing.Additionally,the contents of Al,MDA and H₂O₂ in RB roots were significantly decreased while 50 μmol·L^-1 IAA was added to 25,50 and 200 μmol·L^-1 Al treatment solutions.Furthermore,the citrate exudation increased approximately 2.39,1.73 and 6.85-fold and the activities of the PM H⁺-ATPase enhanced approximately 1.09,1.74 and 1.45-fold than that of only Al treatment in RB roots,respectively.Taken together,our results indicated that exogenous application of IAA significantly enhanced Al resistance of RB by enhancement of citrate exudation and the PM H⁺-ATPase activity under Al stress.