Abstract: A new water-soluble polymeric selective chelating agent for mercury(Ⅱ) was prepared by the acid mercaptalation of the aldehyde derivative of dex-tran with ethylene glycol dithioglycolate. The product is composed of macro-cyclic mercaptal groups linked to dextran. A preliminary examination of its acute toxicity and its ability to offset-acute mercuric chloride poisoning has been made. The results indicate that this chelating agent is relatively non-toxic and improves the survival rate of animals.It seems promising as an oral agent for the treatment of mercury poisoning and should be able to remove mercury from the enterohepatic circulation and increase its rate of excretion via the feces and urine.