Sulfasalazine has been used in the treatment of inflammatory bowel disease for over 60 years. Although the drug is frequently associated with gastrointestinal adverse effects, pulmonary adverse effects are very rare. Herein, we report a case of interstitial fibrosis resulting from 4-month sulfasalazine therapy for ulcerative colitis in a patient under long-term follow-up in our clinic due to chronic obstructive pulmonary disease.