O,O ' -Didecanoylchitosan chemically modified with functional groups of dithiocarbamate was prepared. The extent of the immobilization of the functional groups onto one glucosamine unit of chitosan was 96%. It was soluble not only in chloroform and toluene but also in hexane and kerosene. Its solvent extraction behaviors for some base metal ions were examined. The order of the selectivity to these metal ions was found to be as follows: Cu(II)much greater than Ni(II)much greater than Fe(III)> Co(II)> Zn(II). The high selectivity to copper and nickel over iron is noteworthy.