Environmental microorganisms have been widely applied in heavy metal remediation. Successful application of the fungi depends on their tolerance to heavy metals. Pb is the one of the most common heavy metals in contaminated environments. We hence explored the mechanisms of lead tolerance between two typical filamentous fungi, A. niger and P. oxalicum. The mechanisms of reducing the Pb toxicity by the two fungi have three major pathways. First, secreted oxalic acid reacts with Pb (II) to form insoluble Pb minerals. Second, the enhanced biosorption via new border of cell wall could prevent Pb (II) transported into hypha. Finally, fungal activity could be maintained even at high Pb concentration due to the intracellular accumulation. Moreover, A. niger has the higher Pb tolerance (up to 1500 mg/L Pb level) compared with P. oxalicum (up to 1000 mg/L). Pb levels below 1000 mg/L partially stimulate the bioactivity of A. niger, which is confirmed by its elevated respiration (from 53 to 63 mg C L^-1 medium h^-1). This subsequently enhanced some functions of A. niger to resist Pb toxicity. A better understanding of Pb tolerance of these two fungi sheds a bright future of applying them to remediate lead-contaminated environments.