To provide the above external preparation composed of a drug-active component consisting of tannic acid and aluminum potassium sulfate and an external preparation base component, having high safety, free from inflammatory action, exhibiting excellent absorbability through the skin and mucosa and useful for the treatment of lesional abnormal tissue of rectum and anus.

This preparation is composed of (A) a drug-active component consisting of (A1) tannic acid and (A2) aluminum potassium sulfate and (B) an external preparation base component such as a liquid base capable of solubilizing the component A, an organic solid or a surfactant. For example, the component A containing 10-90wt.% of the component A2 (based on the component A1) is used in an amount of 0.2-60wt.% based on the component B. The external preparation is preferably used in the form of ointment, cream, lotion or spray.