Dermatomyositis (DM) is a chronic autoimmune microangiopathy. Accurate quantification of muscular microcirculation can assist in early diagnosis and improve clinical outcomes. Inflow-based vascular-space-occupancy (iVASO) is a novel perfusion technique without the need for exogenous contrast agents. This study aimed to determine the potential diagnostic value of iVASO-MRI for patients with DM. The results showed decreased arteriolar muscular blood volume (MBVa) in DM patients, which worsens with the progression of disease, and the diminished MBVa in morphologically-normal appearing muscles. This suggests that iVASO-derived MBVa has the potential to be used as a biomarker for early diagnosis of DM.