Abstract: The present invention relates to reduction of side effects of diclofenac or a salt thereof An agent for reducing side effects of diclofenac or a salt thereof which comprises ornoprostil. It is expected that a combination agent of diclofenac or a non-toxic salt thereof and ornoprostil is comparable to even superior to marketed diclofenac tablets or Arthrotec tables in effects and fast-acting property while showing little side effects (particularly digestive disorders, gastric ulcer, diarrhea/vomiting and renal disorder) and exerting excellent antipyretic, analgesic and antiinlfammatory effects. Also, by formulating the combination agent into a preparation of separation type pharmaceutical preparation, the stability of ornoprostil can be improved.