To obtain highly efficient adsorbents that were insoluble in acidic and basic aqueous solutions, we synthesized new types of crosslinked chitin derivatives (carboxymethylchitin and carboxymethylchitosan) with ionizing radiation, and we investigated the sorption of Cu(II) ions onto these crosslinked chitin derivatives. Sorption kinetic studies indicated the rapid removal of copper(II) ions from the aqueous solutions. Also, isothermal sorption data revealed that Cu(II) was removed by these crosslinked carboxymethylated chitin derivatives with high efficiency. Sorption isothermal data were interpreted well by the Langmuir equation. The uptake of Cu(II) ions was 161 mg/g on crosslinked carboxymethylchitin and 172 mg/g on crosslinked carboxymethylchitosan at pH 5.5. A low pH was favorable for Cu(II) desorption. The Cu(II) ions were desorbed from the crosslinked matrix rapidly and completely after a treatment in a diluted HCl solution, and at the same time, the adsorbents were regenerated to be used again to adsorb heavy metal ions. (C) 2003 Wiley Periodicals, Inc.