We report a patient with primary lung adenocarcinoma who had Ewing's sarcoma and was successfully treated with ifosfamide. A 56-year-old Japanese man was referred to the Orthopedic Department of our hospital with a complaint of pain on his hip, ischuria, and dyschezia (vesicorectal disorder). MRI showed a mass in the sacrum. Open biopsy revealed Ewing's sarcoma (T2N0M0G4, Stage II B). Chest CT to screen showed an abnormal shadow in the left pulmonary lower lobe (S10). Bronchoscopic examination revealed primary lung adenocarcinoma(cT2N0M0, Stage I B). Because of a severe hip pain, treatment for Ewing's sarcoma by high-dose ifosfamide (day 1: 4 g/m2/day --> day 2-7: 2 g/m2/day: total 14 g/m2) was given in one course before lung surgery. The lung adenocarcinoma became small, the reduction ratio of the tumor was 26.5% and the tumor changed into a cavity. No serious adverse effect was observed.