Biosorption of metal ions with Penicillium chrysogenum mycelium is described in this article. Alkaline pretreatment was used to remove proteins and nucleic acids from cells, and this treatment increased the adsorption capacities, for Cr3+ from 18.6 mg g(-1) to 27.2 mg g(-1), for Ni2+ from 13.2 mg g(-1) to 19.2 mg g(-1), for Zn2+ from 6.8 mg g(-1) to 24.5 mg g(-1). The adsorption of metal ions was strongly pH dependent. The mycelium could be used for large-scale removal of Cr3+ from tannery wastewater. The results show that this inexpensive mycelium adsorbent has potential in industry because of its high adsorption, capacity. The main chelating sites are amino groups (-NH2) of chitosan in the mycelium. A new model is established, which describes the relation of adsorption of metal ions on pH according to amino group chelating with metal ions and H+. The relative errors of simulation for Cu2+, Ni2+, Zn2+, and Cr3+ are 4.66%, 5.45%, 11.55%, and 1.69%, respectively.