Abstract: In the present study, the biosorption of nickel ions from aqueous solutions by powder of waste activated sludge was studied. The effect of contact time, pH and shaking rate were investigated. Pseudo-second-order model described the biosorption kinetics better than the Lagergren model. Kinetic experiments showed that nickel concentrations reached equilibrium within 2 h. We found that the biosorptive capacities were dependent on nickel solution pH, with pH 4 being optimal. The influence of the shaking rate on the biosorption capacity of the biomass shows that an optimum value can be obtained between 150 to 250 rpm. The Langmuir isotherm model was applied to experimental equilibrium data of nickel biosorption. The result showed that maximum nickel adsorption capacity of powder of waste activated sludge (qmax) was 11.442 mg g-1 and the Langmuir constant (kd) was 13.9611 mg L-1.