Chronic graft-versus-host disease (GVHD) is a well-known complication of allogeneic bone marrow transplantation (BMT) and has heterogeneous manifestations, with multi-organ involvement. Recently, polymyositis (PM) was reported to be a rare manifestation of chronic GVHD. Here, we report a 30-year-old woman who was diagnosed with PM after allogeneic BMT.