Pyomyositis is a purulent infection of skeletal muscle characterized by fever, localized muscle pain and stiffness, swelling and tenderness. Hematological disorder is one of the predisposing conditions for the development of pyomyositis. A 54-year-old man developed methicillin-resistant Staphylococcus aureus pyomyositis during drug-induced pancytopenia. Debridement of the infection foci combined with antimicrobial agents proved effective even in the advanced stage of the disease. In patients with hematological disorders, pyomyositis should be considered when evaluating local myalgia and high fever because this disease can be very difficult to identify and can become rapidly progressive under a myelosuppressive condition.