To investigate the changes and clinical significance of the levels of Th17/Treg cell subsets in peripheral blood of patients with acute ischemic stroke (AIS). Methods: Based on fulfillment of recruitment requirements, 190 AIS patients were included in the observation group and 60 healthy subjects into the control group. AIS patients were further divided according to the NIH Stroke Scale (NIHSS) into the mild subgroup (61 cases), moderate subgroup (64 cases), and severe subgroup (65 cases). The observation group was also divided according to the modified Rankin Scale (mRS) score into the good prognosis subgroup (139 cases) and poor prognosis subgroup (51 cases). The levels of Th17/Treg cells in the peripheral blood of AIS patients and healthy subjects were detected by flow cytometry. The related cytokines (IL-17, TGF-β) were detected by enzyme-linked immunosorbent assay. The differences in the above indicators were compared in the different severity subgroups and prognostic subgroups, and the predictive value of Th17/Treg cell levels for poor prognosis in patients with AIS was evaluated. Results: The peripheral blood levels of Th17, Th17/Treg cell ratio, and IL-17 in the observation group were significantly higher than those in the control group (P<0.05), while the levels of Treg cell sub- sets and TGF-β were significantly lower than those in the control group (P<0.05). The Th17, Th17/Treg cell ratio, and IL-17 levels in the severe subgroup were the highest; those in the moderate subgroup were the second; and those in the mild subgroup were the lowest (P<0.05). The levels of Treg cells and TGF-β in the severe subgroup were the lowest, the moderate subgroup the second, and the mild group the highest (P<0.05). The peripheral blood levels of Th17, Th17/Treg cell ratio, and IL-17 in the poor prognosis subgroup were significantly higher than those in the good prognosis subgroup (P<0.05), while the levels of Treg cell subsets and TGF-β were significantly lower than those in the good prognosis subgroup (P<0.05). ROC curves analysis showed that Th17 cell and Treg cell levels in peripheral blood had 78.01% and 79.17% sensitivity and 82.50% and 74.50% specificity, respectively, in predicting poor prognosis in patients with AIS. Conclusion: The Th17/Treg cell subsets in peripheral blood are closely related to the severity and prognosis of AIS, and they have certain value in clinical application for the assessment of severity and prognosis in AIS patients.