The effects of temperature, pH, chitin and chitosan on Pb2+ removal by crab shell were investigated. Pb2+ removal by crab shell was greater than that of chitin and chitosan, indicating that chitin did not contribute to Pb2+ removal by crab shell. The quantity and rate of Pb2+ removal increased as the pH value increased. The rate of Pb2+ removal increased with increased temperature, but the maximum amount of Pb2+ removal was constant irrespective of temperature. Metal ions (K+, Na+, Mg2+, Ca2+) were released from crab shell concomitant with Pb2+ removal by ion exchange. The amount of Ca2+ released was greater than any for other metal ions in both Pb2+ and Pb2+-free solutions. The amount of Ca2+ released in Pb2+ solution was greater than that in Pb2+-free solution, whereas CO32-release in Pb2+ solution was less than in Pb2+-free solution. Pb2+ removal was mainly a consequence of dissolution of CaCO3(s) with consequence precipitation of Pb-3(CO3)(2)(OH)(2(s)) and PbCO3(s). Pb2+ accelerated the dissolution of CaCO3(s) by ion exchange and the precipitation occurred both at the surface and in the inner part of the crab shell.