To provide a patch containing fentanyl for mucous membrane of the oral cavity (oral transmucosal fentanyl), which rapidly increases the serum concentration of the drug, is easy in handling and is superior in safety. The patch can be prepared by laminating on one side of a drug layer which contains fentanyl or its salt as an active ingredient, methyl vinyl ether-maleic anhydride copolymer as an adhesive, and at least one substance selected from the group consisting of hydroxypropylcellulose, hydroxypropylmethylcellulose and hydroxyethylcellulose as a thickener, a support layer hardly soluble or insoluble in water, and a backing in this order.