PURPOSE: To obtain the subject hardening agent for treating lesion of digestive organ containing an inorganic acid or organic acid and its salt, a water-soluble zinc compound, an alcohol and water, being stable, not causing precipitation, insoluble foreign matter and coloring and having clear appearance.

CONSTITUTION: (A) An inorganic acid (e.g. sulfuric acid) or an organic acid (e.g. citric acid) and its salt are blended with (B) a water-soluble zinc compound (e.g. zinc sulfate), (C) an alcohol (e.g. benzyl alcohol) and (D) water and further, as necessary, (E) an antioxidant (e.g. sodium hydrogen sulfite), (F) an antiseptic and analgesic agent (e.g. tannin) and (G) polysaccharides which are auxiliary components for enhancing viscosity of the preparation (e.g. dextran) are added to the blend to provide the objective uniform and clear hardening agent for treating lesion of digestive organ such as hemorrhoid, polyp of colon, prolapse of rectal mucous membrane, proctocele, rectal ulcer or hepatic tumor and being stable and not causing precipitation, formation of insoluble foreign matters and coloring even if it is stored for a long period.