A 46-year-old man was admitted for the evaluation of a dry cough and dyspnea on exertion. Laboratory tests revealed anemia, elevated CRP, polyclonal hyperimmunoglobulinemia, and an elevated interleukin-6 level. Radiological examination of the chest showed peribronchovascular consolidations, ground glass opacities, small nodular opacities, and interlobular septal thickenings in the lungs, accompanied with hilar and mediastinal lymphadenopathies. A video-assisted thoracoscopic lung and mediastinal lymph node biopsy revealed plasmacytic and lymphocytic infiltration around the bronchovascular bundles of the lungs, and plasmacytic infiltration in the interfollicular areas of the nodes. Based on these findings, a diagnosis of multicentric Castleman disease was confirmed. The patient received a humanized anti-interleukin-6 receptor antibody, (tocilizumab, 8 mg/kg), every 2 weeks for 3 years, during which time, his PaO2 level improved from 64.1 Torr to 83.4 Torr, vital capacity increased from 2.53 L to 3.95 L, and radiological abnormalities in the lungs gradually improved, suggesting that tocilizumab is effective for interstitial pneumonia in patients with multicentric Castleman disease.