A low-molecular polysulfated hyaluronic acid derivative useful in the prevention and/or treatment of allergic diseases.Provided is a preventive and/or therapeutic agent for an allergic disease selected from pollinosis, allergic rhinitis, allergic conjunctivitis, atopic dermatitis, and asthma, the agent containing either a low-molecular polysulfated hyaluronic acid derivative represented by general formula (IA) or (IB) or a pharmaceutically acceptable salt thereof as an active ingredient.[In the formulae, n is a number of 0-15, and Rs each independently represents a hydrogen atom, an SO
