A hydroponic experiment was carried out to study the effect of aluminum (A1) and cadmium (Cd) on AI and mineral nutrient contents in plants and Al-induced organic acid exudation in two barley varieties with different Al tolerance.Al- sensitive cv.Shang 70-119 had significantly higher Al content and accumulation in plants than Al-tolerant cv.Gebeina, especially in roots, when subjected to low pH (4.0) and Al treatments (100μmol L~(-1) Al and 100μmol L~(-1) Al+1.0μmol L~(-1) Cd).Cd addition increased A1 content in plants exposed to A1 stress.Both low pH and Al treatments caused marked reduction in Ca and Mg contents in all plant parts,P and K contents in the shoots and leaves,Fe,Zn and Mo contents in the leaves,Zn and B contents in the shoots,and Mn contents both in the roots and leaves.Moreover,changes in nutrient concentrations were greater in the plants exposed to both Al and Cd than in those exposed only to Al treatment. A dramatic enhancement of malate,citrate,and succinate was found in the plants exposed to 100μmol L~(-1) Al relative to the control,and the Al-tolerant cultivar had a considerable higher exudation of these organic acids than the Al-sensitive one,indicating that Al-induced enhancement of these organic acids is very likely to be associated with Al tolerance. A hydroponic experiment was carried out to study the effect of aluminum (A1) and cadmium (Cd) on AI and mineral nutrient contents in plants and Al-induced organic acid exudation in two barley varieties with different Al tolerance. Al-sensitive cv.Shang 70-119 had significantly higher Al content and accumulation in plants than Al-tolerant cv. Gebeina, especially in roots, when subjected to low pH (4.0) and Al treatments (100 μmol L -1 Al and 100 μmol L ~ (- 1) Al + 1.0μmol L ~ (-1) Cd). Cd addition increased A1 content in plants exposed to Al stress.Both low pH and Al treatments caused marked reduction in Ca and Mg contents in all plant parts, P and K contents in the shoots and leaves, Fe, Zn and Mo contents in the leaves, Zn and B contents in the shoots, and Mn contents both in the roots and leaves. More over, changes in nutrient concentrations were greater in the plants exposed to both Al and Cd than in those exposed only to Al treatment. A dramatic enhancement of malate, citrate, and succinate was f ound in the plants exposed to 100 μmol L -1 Al relative to the control, and the Al-tolerant cultivar had an appreciably higher exudation of these organic acids than the Al-sensitive one, indicating that Al-induced enhancement of these organic acids is very likely to be associated with Al tolerance.