A 40-year-old man was diagnosed with Langerhans cell histiocytosis (LCH) in October 2010. His LCH was refractory to conventional chemotherapy, and thus worsened to Langerhans cell sarcoma (LCS) in May 2011. Although we repeated combination chemotherapies, new infiltration of the liver and bone marrow, as well as primary lesions of the bone, lymph nodes, and skin, appeared. These intensive chemotherapies caused candida liver abscesses, invasive aspergillosis, disseminated varicella zoster virus infection and bacterial sepsis. We administered bendamustine for chemotherapy, which resulted in a partial response (PR) with no severe adverse events. Because of pancytopenia caused by secondary myelodysplastic syndrome, we stopped the bendamustine chemotherapy after two courses. PR was maintained for 4 months. We plan to perform allogeneic hematopoietic stem cell transplantation from a sibling donor after a conditioning regimen. Optimal therapy for adult LCH, which is a rare and treatment-resistant disease, has yet to be established. Bendamustine is a potential chemotherapeutic agent for standard treatment of LCS.