The adsorption of dyes in the solutions using activated sludge might be a promising approach in wastewater treatment units. The adsorption of Basic Red 18 and Basic Blue 9 from aqueous solution by dried activated sludge was investigated with in a batch system. The activated sludge had the highest dye uptake capacity, having the monolayer adsorption capacity 285.71 and 256.41 mg g(-1) for Basic Red 18 and Basic Blue 9, respectively, at pH value of 7.0 and 20degreesC. Langmuir and Freundlich adsorption models were used for the mathematical description of the adsorption equilibrium and the equilibrium data fixed very well with both the Langmuir and Freundlich models. The R-L values showed that, activated sludge was favorable for the adsorption of basic dyes. The suitability of the kinetic models for the adsorption of dyes on the activated sludge was also discussed. It was clear that the adsorption kinetics of dyes to dried activated sludge obeyed pseudo second-order adsorption kinetics. (C) 2004 Elsevier B.V. All rights reserved.