Abstract:［Objective］Ectomycorrhizal fungi (ECMF)，important components in forest ecosystems，could form symbionts with wooden plant roots and participate in nutrient absorption.［Methods］Boletnus sp.(Bo 07)，Lactarius delicious (Ld 03) and Pisolithus tinctorius (Pt 715) isolated from Southwest China and Cenococcum geophilum (Cg 04) from Daqing Mountain，Inn Mongolia，China，were cultured in liquid Pachlewsk medium at 25 1℃ for 28 days with soil as sole K source．Fungal biomass，K uptake，efflux of protons and organic acids，and changes of soil K pools were measured to study K mobilization from soil by ECMFs.［Results］The fungal biomass，K concentration and uptake of Bo 07，Ld 03 and Pt 715 were much higher than Cg 04，indicating their strong abilities to absorb K and to adapt low K environment by bio-evolution and selection．K concentrations in culture solution were increased by ECMFs compared to blank control (without ECMF)．ECMFs could promote K release from the soil into culture solution． Bo 07，Ld 03 and Pt 715 increased significantly exchangeable K in soils，while structural K in soil was decreased by Bo 07 and Ld 03．They could thus mobilize unavailable K from ［Conclusion］ECMF isolates could mobilize unavailable K in soils．