The sorption behavior of biosorbent prepared from paddy straw with nine different heavy metals has been studied. The binding mechanisms involving adsorption and the cation-exchange process have also been investigated. Characterization of biosorbent through a scanning electron microscope revealed no major surface deformity resulting from the chemical treatment. X-ray photo electron spectroscopy was also used to determine the presence of exchangeable cations in the sorbent and the speciation of bound chromium, cadmium, and mercury. The maximum sorption capacity (millimoles/gram) obtained from the Langmuir model for Pb2+, Cd2+, Hg2+, Co2+, Ni2+, Mn2+, Zn2+, and Cu2+ were 0.286, 0.147, 0.226, 0.181, 0.196, 0.189, 0.219, and 0.248, respectively. Interpretation of Dahlquist (1978) and Scatchard (1949) was also used for the binding site heterogeneity. The unique ability of the biosorbent to bind nine different metals has been attributed to the presence of surface heterogeneity and Ca2+ ions, which attract and sequester metal ions. Biosorption results are useful for the development of low-cost biosorbent.