Extracellular vesicles (EVs) have been implicated in dermatomyositis pathogenesis, but their protein content is not well characterized. We collected EVs from plasma, isolated them using sequential ultracentrifugation and size-exclusion chromatography, and analyzed their content by mass spectrometry. Protein biomarkers that distinguish patients with DM from controls were assessed using the random forest algorithm. Out of these, select proteins were identified as highly potential disease biomarkers, and their abundance was confirmed in a separate cohort using ELISA. Thirty-five proteins were differentially expressed and 67 were uniquely detected in the patient cohort. The following proteins displayed the most significant differential expression and were validated in a separate cohort of patients: The antioxidant enzyme glutathione peroxidase 3 (GPX3), and two complement proteins, Ficolin-2 (FCN2) and SERPING1 were less abundant in patients' EVs. Surfactant protein B (SFTPB) was expressed almost exclusively in patients with lung disease, suggesting that it may be a marker for pulmonary involvement. In summary, we identified GPX3, FCN2 and SERPING1 as biomarkers in DM. Our data underline the importance of oxidative stress and complement regulation in DM. SFTPB is a potential biomarker for pulmonary involvement.