Several effects on Pb^2+ removal by crab shell from aqueous solution were investigated. As the increase of initial Pb^2+ concentration and decrease of initial crab shell concentration, the time required to reach an equilibrium state and the residual Pb^2+ concentration increased. In our experimental ranges, the optimum initial Pb^2+ concentration and crab shell concentration were below 103 mg/1 and over 0.5 mg/l, respectively. Also, in order to investigate the mechanism of Pb^2+ removal by crab shell in aqueous solution, the crab shell was compared with chitosan and chitin on aspects of Pb^2+ removal capacity and Pb^2+ removal rate. The Pb^2+ removal by crab shell was greater than that by chitin and chitosan. The role of chitin was not so great in Pb^2+ removal by crab shell. The Pb^2+ removal by chitosan was not exactly correlated to the molecular weight of chitosan.