In order to investigate the function of Ca2+ in the alleviation of Al3+ stress in ectomycorrhizal fungi, four strains (Bo 02, Bo 15, Pt 715 and Sl 08) were grown in liquid culture media to study the Al resistance of different strains and the effect of exogenous Ca2+ (0, 0.25, 0.5, 1.0 mmol x L(-1)) on the activity of antioxidative protective enzymes under Al3+ stress. It was showed that ectomycorrhizal fungal species varied in resistance to Al3+ stress. Pt 715 and Sl 08 were more tolerant to Al3+ than Bo 02 and Bo 15 in vitro. The activities of CAT and SOD in Bo 02, SOD in Bo 15, CAT and POD in Sl 08 increased significantly under Al3+ stress. It was showed that the activities of these enzymes in ectomycorrhizal fungi had a close relationship with Al3+ stress. The enzymes in Bo 02 were most sensitive to exogenous Ca2+ and the function of Ca2+ in resisting Al3+ stress was the best in the four strains. A high concentration of Ca2+ (> or = 0.5 mmol x L(-1)) could alleviate or offset the increased activities of antioxidative protective enzymes by Al3+ stress in Sl 08.