Objective: To investigate the protective effect and immune mechanism of berberine on cerebral ischemia/reperfusion injury in rats. Methods: Fifty SD rats were randomly divided into sham operation group (Sham), model group (Model), berberine low dose groups (BBR-L, 25 mg/kg), berberine medium dose groups (BBR-M, 50 mg/kg) and berberine high dose groups (BBR-H, 100 mg/kg), with 10 rats in each group. Longa suture method was used to establish a rat model of cerebral ischemia/reperfusion, after 2 hours of ischemia, reperfusion for 24 hours. Rats in BBR-L, BBR-M and BBR-H were treated with berbrerine by gavage 2 hours after successful model building, while the sham operation group and the modle group were given the same volume of saline as described above. After 24 hours of administration, the activity of antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), cytokine tumor necrosis factor α (TNF-α) , interferon β (IFN-β) , interleukin 6 (IL-6) and nitric oxide (NO) content were detected by ELISA assay. Serum CD4+, CD8+ and CD4+/CD8+ contents were measured by flow cytometry to investigate the immune function of each group. RT-qPCR and Western blot were used to detect NF-kappaB-NOD-like receptors 3 (NF-κB-NLRP3) signal axis key genes and protein expression in rat brain tissue. Results: Compared with the sham operation group, the degree of neurological deficit and the rate of cerebral infarction were increased in the model group (P＜0.05), and the levels of serum NO, TNF-α, IFN-β, IL-6, NF-κB p65, NLRP3, ASC and caspase-1 in brain tissue were increased (P＜0.05), while the activities of SOD, GSH-Px and the levels of CD4+, CD8+ and CD4+/CD8+ in serum were decreased (P＜0.05). Compared with the model group, the degree of neurological deficit and the rate of cerebral infarction were increased in the BBR-H, BBR-M and BBR-L groups (P＜0.05), and the levels of serum NO, TNF-α, IFN-β, IL-6, NF-κB p65, NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC) and caspase-1 in brain tissue were increased (P＜0.05), while the activities of SOD, GSH-Px and the levels of CD4+, CD8+ and CD4+/CD8+ in serum were decreased (P＜0.05). Conclusion: Berberine may reduce oxidative stress, inhibit inflammation, enhance immune function, and reduce cerebral ischemia/reperfusion injury in rats, which may be related to the inhibition of NF-κB-NLRP3 signaling.