Traumatic brain injury (TBI) is associated with trauma-related death. In this study, we evaluated differences in the expression of plasma microRNAs (miRNAs) in patients with different degrees of TBI, and explored the potential of miRNAs for use as diagnostic TBI biomarkers. The miRNA microarray results showed upregulation of 65, 33, and 16 miRNAs and downregulation of 29, 27, and 6 miRNAs in patients with mild, moderate, and severe TBI, respectively, compared with healthy controls. Thirteen miRNAs (seven upregulated and six downregulated) were found to be present in all TBI groups. Seven upregulated miRNAs were selected for validation in an enlarged cohort of samples and showed good diagnostic accuracy. The expression levels of miR-3195 and miR-328-5p were higher in the severe TBI group than in the mild and moderate TBI groups. In summary, our study demonstrates different expression profiles in plasma miRNAs among patients with mild to severe TBI. A subset of seven miRNAs can be used for diagnosis of TBI. Moreover, miR-3195 and miR-328-5p may be utilized during diagnosis to distinguish mild and moderate TBI from severe TBI.