Eosinophilic fasciitis (EF) is a rare connective tissue disease characterized by erythema and painful edema on extremities, followed by induration of the skin, with laboratory findings of peripheral eosinophilia, hypergammaglobulinemia. Histopathological findings in EF include increased thickness of the fascia with infiltration of lymphocytes, plasma cells, mast cells, eosinophils. The differential diagnosis includes scleroderma, morphea and any panniculitis. A 34-year-old man presented with stiffness of upper extremities for five months. The patient also complained of lesional pain and decreased mobility of the wrist and elbow joint that had occurred a month later. Left forearm MRI showed diffuse fascial T2 hyperintensity with enhancement along the deep and intermuscular fascia. Histopathologic findings revealed thickened fascia with infiltration of eosinophils, lymphocytes and plasma cells, and also showed myopathic change. The patient was diagnosed as EF with polymyositis, based on the clinical characteristics and histopathologic findings. Lesional pain and joint mobility was gradually improved after 10 months of systemic steroid and immunosuppressant. To our knowledge, EF is a rare disease and only 4 cases have been reported in Korean dermatology literature. Moreover, the case of EF with polymyositis has not been reported in Korea before. So we herein report a rare case of EF in a patient with polymyositis.