In this study, the biosorption of Malachite Green, a cationic dye from aqueous solution onto pretreated biomass of Penicilium sp. was examined. The biosorption studies were carried out under various parameters such as initial pH, contact time and initial dye concentration. The experimental results show that optimum pH for efficient dye biosorption was found to be 5.0-6.0 for pretreated biomass. The bosorption capacity was increased with the increasing initial dye concentration in studied dye concentration range. The kinetic data obtained at different concentrations were analyzed using pseudo-first-order, pseudo-second-order and intra-particle diffusion models. It was obtained that the biosorption process followed the pseudo-second-order kinetic model.