In this paper, orange peel modified with different chemical reagents as biosorbents were used to remove cadmium ion from aqueous solution. Effects of different chemical modifications on the biosorbent properties including washing, alkali saponification, cross-linking temperature and concentration of cross-linking reagent were investigated. Meanwhile, influence of pH of solution, initial cadmium concentration, shaking time and solid/liquid ratio on the removed of Cd(II) by different chemically modified biosorbents were studied. It can be concluded that cadmium ion could be removed by 0.6SCA(80) (orange peel modified with 0.6 mol L-1 citric acid under 80 degrees C after alkali saponification) biosorbent effective and quick. We obtained a series of biosorbents with the order of cadmium: 0.6SCA(80) > SOP > CA2 > CA1 > PA1 > PA2 > OP. For 0.6SCA(80), the maximum capacity of cadmium was 0.90 mol kg(-1), the optimum pH value was 6, the reaction balance was established after shaking 120 min and the optimum solid/liquid ratio was 4.3 g L-1. The desorption rate of cadmium was 94% with 0.15 mol L-1 HCl solution. A comparison of different isotherm models revealed that the Langmuir isotherm model is fitted the experimental data best. The biosorption follows the Lagergren first-order kinetics model. (c) 2006 Elsevier B.V. All rights reserved.