A low-molecular-weight polysulfated hyaluronic acid derivative useful for prevention and/or treatment of an allergic disease. An agent for prevention and/or treatment of an allergic disease selected from pollinosis, allergic rhinitis, allergic conjunctivitis, atopic dermatitis, and asthma, represented by the following general formula (IA) or (IB)； wherein n represents a number of 0 to 15； R's each independently represent a hydrogen atom or an SO 3 H group etc.
