Abstract: The stable isotope ⁵⁶Fe was used to simulate the radioactive ⁵⁵Fe, ⁵⁹Fe, and ⁵²Fe ions existing in the wastewater generated by nuclear medicine and then the removal efficiency of ⁵⁶Fe²⁺ in water was studied using chitosan functionalized multi-walled carbon nanotubes (CS-MWNTs) as adsorbent. The influences of pH, temperature, time, and equilibrium ion concentration on the adsorption capacity were studied. The results show that in the same conditions, the adsorption capacity of CS-MWNTs is significantly increased compared to the pristine multi-walled carbon nanotubes (MWNTs). Both CS-MWNTs and MWNTs exhibit a better removal efficiency of Fe²⁺ in neutral solutions than in acidic solutions, while in basic solutions, the Fe²⁺ will precipitate and the removal of Fe²⁺ is no longer due to the adsorption effect. The adsorption equilibrium will be reached in about 3 h and the adsorption of Fe²⁺ to either CS-MWNTs or MWNTs is endothermic. At room temperature of 25 ℃ and pH＝5, the saturate adsorption capacity of CS-MWNTs for Fe²⁺ is 51 mg/g, and that of pristine MWNTs is 27 mg/g. The Freundlich adsorption model can well represent the adsorption of Fe²⁺ to both of two kinds of adsorbent materials.