A 41-year-old woman had undergone a left mastectomy breast cancer three years prior to presentation. No for at six months she had recurrence, this time in the right breast and skin. Despite first-and second-line chemotherapy, the mass showed progression of the disease. Thereafter, a weekly treatment of vinorelbine and trastuzumab was started, but one month later, she developed a slight fever and dry cough. A chest CT scan revealed an infiltration shadow showing non-specific interstitial pattern in the right lung. A bronchoscopic examination showed lymphocyte dominance in bronchial lavage fluid, and lymphocyte infiltration into the interstium with fibrosis in the tissue specimens was found by transbronchial lung biopsy. After discontinuing the above vinorelbine therapy, the patient's condition improved. We therefore diagnosed this as a case of vinorelbine-and trastuzumab-induced interstitial pneumonia.