Abstract: To understand the roles of organic acids and mycelium adsorption in Al-resistance, two species of ectomycorrhizal fungi (ECMF), namely Lactarius deliciosus strain 2 (Ld 2) and Pisolithus tinctorius strain 715 (Pt715) with the ability of Al-resistance ranked as Ld 2 >Pt 715, were cultured in acidic medium with or without Al³⁺. Organic acids and Al³⁺ concentrations in medium were examined after 21 d. Results showed that organic acids in culture medium were different between the species of ECMF. It was ranked as formic acid > oxalic acid in Ld 2 culture medium, whilst as tartaric acid > formic acid > oxalic acid > succinic acid inPt 715 culture medium, whether the two ECMF were cultured with or without Al addition. Moreover, Al³⁺ addition significantly increased both formic acid and oxalic acid secreted by Ld 2, whilst both tartaric acid and formic acid secreted by Pt715. Al³⁺ absorption by the two ECMF was active, which followed the kinetic model of ion absorption. The CEC,C_min, I_max, and adsorptive Al³⁺ in Ld 2 mycelium were higher than in Pt 715 mycelium. In contrast, both the K_m and absorptive Al³⁺ were lower inLd 2 mycelium than in Pt 715 mycelium. Therefore, both organic acids secretion and Al³⁺ adsorption by mycelium were important in Al resistance of ECMF. They may act in different ways. On the one hand, organic acids secretion could contribute to the activation and utilization of nutrients. On the other hand, Al³⁺ adsorption by mycelium could prevent Al³⁺ from entering the symplast.