The potential use of the fungus Penicillium purpurogenum to remove cadmium, lead, mercury, and arsenic ions from aqueous solutions was evaluated. Biosorption of heavy metal ions reached equilibrium in 4 h. Heavy metal ions binding by Penicillium purpurogenum was clearly pH dependent. Heavy metal loading capacity increased with increasing pH under acidic conditions, presumably as a function of heavy metal speciation and due to the H+ competition at the same binding sites. The adsorption of heavy metal ions reached a plateau value at around pH 5.0. The maximum adsorption capacities of heavy metal ions onto the fungal biomass under noncompetitive conditions were 35.6 mg/g for As(III), 70.4 mg/g for Hg(II), 110.4 mg/g for Cd(II) and 252.8 mg/g for Pb(II). Their adsorption behavior can be described at least approximately with the Langmuir equation. The competitive adsorption capacities of the heavy metal ions were 3.4 mg/g for As(III), 15.8 mg/g for Hg(II), 13.1 mg/g for Cd(II), and 41.8 mg/g for Pb(II) at 50 mmol/L initial concentration of metal ions. The same affinity order on a molar basis was observed under noncompetitive and competitive adsorption conditions, which was as follows: Pb(II)>Cd(II)>Hg(II)>As(III). The equilibrium loading capacity of Pb(II) was greater than that of other metal ions. This fungal biomass showed a preference for binding Pb(II) over Cd(II), Hg(II), and As(III). Elution of heavy metal ions was performed using 0.5 M HCl. The fungus Penicillium purpurogenum could be used for ten cycles for biosorption.