Coagulation is one of the most important methods for water treatment, but the main objects of coagulation are only the hydrophobic colloids and suspended particles. In order to remove both soluble heavy metal species and insoluble substances efficiently by coagulation, sodium xanthogenate group was grafted to polyethyleneimine. This new kind of coagulant can be called PEX. The efficiency of PEX was tested by using Ni2+, Cu2+ or Cr6+ and kaoline as the targets. The experiment proved that PEX was an amphoteric polyelectrolyte and its isoelectric point was pH 3.0. When the pH of water sample is lower, PEX is electrically positive, therefore the colloidal substances with negative charges can be coagulated by it, but the cationic Ni2+ ion cannot be removed very well. When the pH of water sample is higher, the positive charge of PEX decreases, but more xanthogenic acid groups ionize to the negative xanthogenate radical, so that the turbidity removal decreases, and the Ni2+ removal increases. (C) 2007 Elsevier Ltd. All rights reserved.