The present invention provides a transdermal delivery system consisting of a backing layer, a drug-containing matrix layer, and a release layer, wherein the drug-containing matrix layer comprises (a) donepezil or a pharmaceutically acceptable salt thereof as an active ingredient, (b) a mixture of high molecular weight polyisobutylene having a weight-average molecular weight ranging from 400,000 to 3,000,000 and low molecular weight polyisobutylene having a weight-average molecular weight ranging from 25,000 to 300,000 as an adhesive, and (c) a permeation enhancer in not more than 3 % by weight based on the total weight of the drug-containing matrix layer.
