Provided is a conjugate including a pharmacologically active substance covalently bound to chitosan or its derivative and a method for transmucosal delivery of a pharmacologically active substance using the same. Specifically a conjugate includes a pharmacologically active substance covalently bound via a linker to chitosan and a pharmaceutical composition for transmucosal administration of a drug includes the aforementioned conjugate and a pharmaceutically acceptable carrier. Further provided is a method for in vivo delivery of a pharmacologically active substance via a transmucosal route, by covalent binding of the active substance with chitosan or its derivative via a linker. The conjugate in accordance with the present invention exhibits excellent absorption rate and biocompatibility in biological mucous membranes, particularly mucous membranes of the alimentary canal (especially the gastrointestinal tract), in vivo degradability, and superior bioavailability even with oral administration, thus enabling treatment of diseases via oral administration of a drug.
