Chitin was isolated from crab shell. Chitosan, which was prepared by the deacetylation of chitin, was acylated to obtain N-acetyl(regenerated chitin), N-propionyl, N-butyryl, N-hexanoyl, N-decanoyl and N-maleated chitosans and their metal ion adsorption characteristics of N-acylchitosans were investigated. In order to enhance the adsorptivity, their porous beads were prepared and their adsorptivity with respect to the porosity and the adsorptivities for metal ions(Cu^(2+), Ni^(2+), Co^(2+), Mn^(2+), Ag^+)were investigated. Their metal ion adsorptivities were remarkably imporved compared to those of chitin. As the larger acyl groups were introduced, adsorptivity increased, but that of N-decanoyl chitosan showed some decrease because of steric hindrance of the bulky N-decanoyl group. N-Maleated chitosan containing carboxyl group showed highly improved adsorptivity, and N-acylchitosans showed the good selective adsorption in the mixed metal ions(Cu^(+2), Ni^(+2), Co^(+2), Mn^(+2) and Ag^+). They also showed excellent adsorption characteristics as chelating polymers.