To obtain the subject pharmaceutical composition as an inhibitor effective as a preventive/therapeutic agent for inflammatory diseases such as chronic arthrorheumatism, arthrosis deformans and arthritis like periarthritis scapulohumeralis, allergic diseases and the like, by inclucing polysulfated hyaluronic acid and others.

This pharmaceutical composition contains, as active ingredient, (A) polysulfated hyaluronic acid or (B) polysulfated dermatan sulfate or a physiologically acceptable salt thereof. The component A or B is prepared, for example, by reaction of hyaluronic acid or dermatan sulfate as a natural mucopolysaccharide, or naturally-occurring dermatan polysulfate, using a complex of sulfur trioxide and pyridine or the like as a sulfation agent, in an appropriate solvent under heating.