We have synthesized the water-insoluble chitosan derivative, N-dithiocarboxy chitosan sodium salt, through the reaction of chitosan with carbon disulfide in the presence of alkali metal hydroxide, Chitosan itself has been prepared using chitin, one of the most abundant compounds in nature, as a starting material. To elucidate this natural polymer the capacity of adsorbing heavy metal ions, we have performed adsorption experiments using chitosan derivatives of various average molecular weights with different contents of sulfur. The effect of pH, adsorption time and temperature on adsorption efficiency was also studied. The adsorbent derived from chitosan of average molecular weight ranging $5,700{sim}20,000$ was shown to have the highest capacity of adsorbing heavy metal ions. Adsorbing efficiency was increased as the reaction time was increased and as the reaction temperature range of $25{sim}45^{circ}C$. The adsorption capacity at various pH, however, appeared to vary depending on the heavy metal ions studied.