A 38-year-old man, diagnosed as having multicentric Castleman’s disease (plasma cell type) in 1995, had been treated with melphalan and prednisolone or prednisolone alone, but there was no remarkable response. In 2002, he was admitted to our hospital with a chief complaint of increasing dyspnea on effort. Laboratory data showed high serum IgG (10050 mg/dl), interleukin-6 (37.9 ng/ml), and vascular endothelial growth factor (VEGF 1920 pg/ml) levels. In addition, serum viscosity was very high (6.0 cp). Electrocardiogram, echocardiogram, and cardiac catheterization demonstrated pulmonary hypertension (PH). There were no other demonstrable causes of PH suggesting that PH was due to hyperviscosity syndrome and high VEGF level. He was treated with plasmapheresis, resulting in a transient improvement of dyspnea. Then, he was given humanized anti-interleukin-6 receptor antibody (tocilizumab), which resulted in the dramatic improvement of dyspnea and PH a few weeks later. PH is a rare complication of MCD, and could be successfully treated with tocilizumab.