Abstract A series of N, O-carboxymethyl-chitosan ( N, O-CMC) with different degree of substitution (DS) were prepared by using chitosan (CTS) and monochloroacetic acid under various conditions. The adsorption properties of N, O-CMC were evaluated. The results revealed that N, O-CMC is suitable for adsorbent to removal Cu(II) ion. The parameters for the adsorption of Cu(II) ions by N, O-CMC were also determined. It was shown that the samples of N, O-CMC had given good correlation with Langmuir's isotherm model and that the adsorption kinetics of Cu(II) could be best described by the pseudo-second-order model. It was also observed that the adsorption capacity seemed to be dependent on pH value in solution, the DS of samples and ionic strength. Furthermore, the maximum adsorption capacity of the monolayer was 162.5 mg of Cu(II) per gram of polymer with DS of 0.96. FTIR and X-ray photoelectron spectroscopy revealed that Cu(II) ions and N, O-CMC formed a chelate complex.