In this study, to select aluminum (Al³⁺)-tolerant ectomycorrhizal (ECM) fungi and study the resistance mechanism of ECM fungi under Al³⁺-stress, 10 ECM fungi strains were selected from different environments and cultivated in liquid media with variable concentrations of Al³⁺ (0, 0.20, 0.40, and 1.00 mmol/L). The biomass, efflux of organic acid, and composition of nutrient elements were measured during cultivation. Of the studied fungal strains, Sl 08 showed the strongest resistance to Al³⁺, while Pt 715, Ld 03, Bo 11, Sl 01, and Bo 15 were also resistant to Al³⁺. The growth of other tested fungal strains (Sl 14, Gc 99, Cg 04, and Sg 11) was obviously inhibited by Al³⁺, but that of Sg 11 was most sensitive to Al³⁺. These results indicated that the ability of ECM fungi to tolerate Al³⁺ toxicity may be closely related to their original growth environments, and fungal strains isolated from acidic soils in south China might be more tolerant to Al³⁺ compared to those isolated from calcareous soils in north China. ECM fungi excrete various organic acids, but the amount and type of these acids vary depending on the fungal strain. For example, ECM fungi could increase the secretion of oxalate to alleviate the effects of Al³⁺ toxicity. In this study, oxalate secretion was observed to increase in the majority of Al³⁺-resistant strains, and the highest oxalate production was observed in the most Al³⁺-resistant strain (Sl 08). The secretion of oxalate was observed to decrease in some fungal strains (Bo 11 and Sl 01) that were still resistant to Al³⁺, whereas oxalate secretion was observed to increase in all Al³⁺-sensitive strains (Cg 04, Sg 11, Sl 14, and Gc 99). This finding suggests that oxalate secretion is not the only pathway through which ECM fungi can alleviate effects of Al³⁺ toxicity. In addition, the fungal strains showed different characteristics in the uptake of nitrogen (N), phosphorus (P), and potassium (K) under Al³⁺ stress. The N, P, or K content in most of the tested fungi increased in the presence of Al³⁺, and only Al-sensitive Sl 14 showed no clear difference in the uptake of N, P, or K under these conditions. The N, P, and K content increased both in the resistant (Pt 715 and Bo 11) and in the sensitive (Cg 04) strains, and the content of two of three elements increased in the resistant (Sl 01, N and K) and sensitive (Sg 11, P and K) strains, respectively. Furthermore, the content of one element (N, P, or K) increased in the resistant (Sl 08, Ld 03, Bo 15) and sensitive (Gc 99) strains. Therefore, it appears that oxalate secretion may be an essential pathway for ECM fungi to tolerate effects of Al³⁺ toxicity. In addition, regulation of the uptake of the nutrient elements, N, P, and K, may be important for ECM fungi to alleviate stress induced by Al³⁺, and increasing the uptake of N, P, and K may be essential for the fungi to tolerate the effects of Al³⁺ stress.