The removal of toxic heavy metal ions (HMI) from aqueous environment has received considerable attention in recent years [1]. Recently, the removal of HMI using functionalized carbon nanotubes was confirmed through experimental investigations [2]. In this work we have studied theoretically the chemical functionalization of (5,0) zigzag single wall carbon nanotube (F-SWCNT) by ethylene-diamin. Afterwards, we have studied the interaction between F-SWCNT and nickel and chromium ions using density functional theory (DFT) method.