A 78-year-old man underwent right lower lobectomy for lung cancer. Histopathological examination led to the diagnosis of adenosquamous cell carcinoma. The background lung adjacent to the pleura showed idiopathic pulmonary fibrosis of microscopic usual interstitial pneumonia pattern, although preoperative computed tomography showed no apparent findings of interstitial pneumonia. The patient showed an acute exacerbation of idiopathic pulmonary fibrosis on the third postoperative day. We herein report a case of acute exacerbation of idiopathic pulmonary fibrosis of microscopic usual interstitial pneumonia pattern after lung cancer surgery.