PROBLEM TO BE SOLVED: To provide a medical tissue adhesive having high adhesive properties, and whose adhesive strength can be reproduced even if being subjected to repeated adhesion.SOLUTION: Provided is a hyaluronic acid derivative having a structure represented by general formula (A) (in the general formula (A), n denotes an integer of 2 or more Ar denotes a hydrocarbon group having the carbon number of 4 or more in Z, one end forms an amido group or an ester group by being integrated with the adjoining carbonyl group, and the other end denotes a functional group capable of forming a bond with the carboxyl group or hydroxyl group of hyaluronic acid, the functional group of the one end and the functional group of the other one end are bonded with a bivalent hydrocarbon group or an oxyalkylene group having the carbon number of 2 to 450).SELECTED DRAWING: None