A case of a 19-year-old man with ulcerative colitis (UC) developed multiple pulmonary nodular shadows with cavity formation, elevated perinuclear antinuclear cytoplasmic antibody (pANCA) and positive lymphocyte stimulation test by drug (DLST) for mesalazine suggesting mesalazine induced Wegener's granulomatosis (WG). Transbronchial biopsy specimens were consistent with WG and thoracoscopic biopsy specimens were consistent with bronchiolitis obliterans organizing pneumonitis (BOOP). We diagnosed WG with BOOP-like variant, which was induced by mesalazine. To our knowledge, this is the first report of a limited form of WG associated with orally administered mesalazine.