There is provided a drug carrier which has solved the problems of conventional drug carriers, which can encapsulate a low molecular drug efficiently, which can control a sustained release period for a long term, which can control blood residence, which has high dispersibility in an aqueous solution, and which is not problematical in safety. A drug carrier, which comprises injectable fine particles minimal in agglomeration between the particles, and which has excellent biocompatibility, is also provided. A hyaluronic acid modification product comprising hyaluronic acid or its derivative, and a polymer bonded together, the polymer being selected from polylactic acid, polyglycolic acid and lactic acid-glycolic acid copolymer, according to the present invention, provides a drug carrier which encapsulates a low molecular drug efficiently, which can control a sustained release period for a long term, which can control blood residence, which is well dispersible in an aqueous solution, and which is not problematical in safety. The hyaluronic acid modification product of the present invention also provides a drug carrier comprising injectable fine particles minimal in agglomeration between the particles, and having excellent biocompatibility.