Background: The elevated plasma mitochondrial DNA (mtDNA) is associated with prognosis in patients with severe acute pancreatitis (SAP). However, it is not clear that the dynamic process of plasma mtDNA during the early stage of SAP and the correction between mtDNA and clinical features.Methods: Twenty-six eligible patients with SAP in the general intensive care unit of our institution were enrolled in this study. The mtDNA concentration were assessed at admission and on days 3, 5, and 7.Results: The mtDNA concentration of the patients with SAP was elevated at each time point compared with that in the healthy controls. The mtDNA levels increased rapidly, peaking on day 3 after admission, and began to decrease on day 5. The trend remained statistically consistent among the acute physiology and chronic health evaluation (APACHE II) score, the sequential organ failure assessment (SOFA) score, C-reactive protein (CRP) levels and mtDNA levels. Contrastingly, the changes were not statistically consistent among the procalcitonin (PCT), calciumion (Ca2+) and mtDNA concentrations. The mtDNA level correlated significantly with the APACHE II score, SOFA score, and Ranson score, but not with the CRP, PCT, and Ca2+ concentrations. Conclusions: The dynamic change of plasma mtDNA correlated significantly with SAP development. The elevated mtDNA levels could be used as a biomarker for the early stage of SAP.Trial registration: NCT: 04079777. Registered 4 September 2019 - Retrospectively registered, https://register.clinicaltrials.gov/prs/app/action/SelectProtocol?sid=S00096E5&selectaction=Edit&uid=U0002O5I&ts=2&cx=-e6bci8