Carboxymethylchitosan (CMChitosan) was prepared by reacting "alkali chitin" with monochloroacetate in 18 w/v% NaOH at 30℃ for 5 hours. The resulting polymer was characterized by IR spectroscopy, acid-base titration and viscometry. The free amino content of the CMChitosan was 1.39 meq/g, and the pKa of the ammonium group in the polymer was 7.0. The amount of carboxylic group in the polymer was 1.42 meq/g. The CMChitosan was soluble in water regardless of pH, and various transition metal ions bind to the polymer even at low pH. In CMChitosan -Cu²⁺ solution, Cu²⁺ -COO- chelate formed in acidic solution, whereas Cu²⁺ -NH₂ chelate was produced at high pH. The cooperativity of Cu²⁺ binding observed in chitosan solution was not revealed in CMChitosan solutions.