Aspergillus niger biomass, obtained as a by-product of fermentation processes, has been tested for lead and mercury sorption. Biomass was produced by two different ways of citric acid production: (a) surface growth, and (b) submerged growth. Their sorption properties have been compared to biomass subjected to an alkaline treatment. The influence of the pH has been studied to select the optimum pH for lead and mercury and pre-select the best sorbent samples. Optimum sorption performances for Pb were obtained with surface-grown biomass which was submitted to alkaline treatment, while with Hg biomass produced by submerged culture was preferred. For lead the experimental pH was set to pH 3, while for mercury the experimental pH was fixed to pH 6. Experiments were continued on selected sorbents by determination of sorption isotherms and uptake kinetics. The influence of experimental parameters (particle size, sorbent dosage, metal concentration) has been checked on sorption kinetics to evaluate the best operating conditions. In the case of lead sorption properties the excellent sorption properties characterized by fast sorption kinetics and high sorption capacities (close to 600 mg Pb g-1) may be explained by the release of a cell component or a by-product of culture procedure (residue of growing media or sub-product of the fermentation process) that induces lead precipitation at long contact time.