The biosorption of phenol, o-chlorophenol and p-chlorophenol from aqueous solutions on dried activated sludge has been investigated. The pollutant binding capacity of the biosorbent was shown as a function of initial pH, initial pollutant concentration and substituted group. The maximum loading capacity of biosorbent was found to be 86.1 mg g(-1) for phenol, 102.4 mg g(-1) for o-chlorophenol and 116.3 mg g(-1) for p-chlorophenol at 100 mg litre(-1) initial pollutant concentration. The Freundlich and Langmuir adsorption isotherms were used for the mathematical description of the biosorption and the isotherm constants were evaluated for each pollutant.