A low-molecular-weight polysulfated hyaluronic acid derivative useful for treatment of an allergic disease. An agent for 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 SO3H group etc.