Polymyositis is uncommon, nonsuppurative Connective tissue disorder. We have experienced a case of polymyositis. Patient was a 20-y.ear old female in good healthy appearance with history of mild, progressive muscle weakness of lower extremities and inability to walk up and down of stairs in recent 3 weeks. Her symptoms were mainly subjective and individual muscle test revealed no abnormalities, but evidences of primary myopathy were easily obtained by muscle biopsy, electromyogram and several enzyme values. We are reporting a case of polymyositis with brief review of literature.