Objective To investigate the clinical characteristics of patients with polymyositis(PM) and dermatomyositis (DM), and compare the differences of PM/DM to help the understanding of clinical diagnosis and treatment. Methods One hundred and forty-five hospitalized PM/DM patients from Department of Rheumatology of the First Affiliated Hospital of Xiˊan Jiaotong University were collected from May 2008 to December 2014, and the clinical manifestations, muscle enzymes, electromyogram, muscle biopsy, treatment outcome were retrospectively analyzed. Mann-Whitney U test and χ2 test were used for statistical analysis. Results The most common initial symptom of PM was muscle weakness, accounted for 51.2%, while rash was the initial presentation in most DM patients(43.1%). The incidence of interstitial lung disease (ILD) (62.7% vs 39.5%, χ2=11.009, P=0.001), and the elevation of CRP (48.9% vs 26.8%, χ2=10.272, P=0.001) were all higher in DM than PM, while the elevation of level of CK (85.4% vs 61.8%, U=-2.668, P=0.008) and CKMB (82.9%vs 41.2%, U=-3.303, P=0.001) were more common in PM compared with DM. The pathological study showed degeneration of muscle fiber, connective tissue hyperplasia in most PM patients, and perimysium atrophy, vacuoles degeneration, muscle bundles, perivascular inflammatory cell infiltration were observed in most DM patients. During the follow-up, the clinical remission rate was 57.5%, the relapse rate and the mortality rate was 7.5%and 31.1%respectively. The mortality rate was higher in DM than PM (34.6% vs 21.4%, χ2=4.861, P=0.027). Infection and tumors were the major causes of death, and the lung was the most common site of infection. Conclusion Differences in the clinical features, muscle enzymes, CRP level, pathology and the mortality rate between PM and DM are evident, while ILD, infection and the higher mortality rate are more common in DM than in PM.