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Background: Cognitive impairment is a common manifestation in patients with T2DM mellitus (T2DM). Ginsenoside Rg1 (GRg1) is the main active substance extracted from ginseng or Panax notoginseng. Methods: T2DM was induced by feeding rats with a high-sugar and high-fat diet combined with a low-dose intraperitoneal injection of streptozotocin (STZ, 35 mg/kg) on an empty stomach. Subsequently, different concentrations of GRg1 (25, 50, 100 mg/kg/d) were used to intervene for 8 weeks and explore its therapeutic effects and potential mechanisms on cognitive impairment in T2DM rats. Results: Our data suggested that administration of GRg1 improved insulin resistance, specifically manifesting in a reduction of insulin resistance index by approximately 57.1 % with high doses of GRg1 (100 mg/kg/d). Besides, it has been observed to lower cholesterol, triglycerides, and low-density lipoprotein by approximately 20–50 % in T2DM rats. In addition, GRg1 treatment dramatically improved the spatial memory and learning ability in T2DM rats. Furthermore, administration of GRg1 to the T2DM rats dose-dependently up-regulated ERKs phosphorylation and blunted phosphorylation of JNKs and p38. Furthermore, GRg1 treatment also dose-dependently increased the expression of Bcl-2 but inhibited the expression of Bax and Caspase 3 expression in T2DM rats brain cortex and hippocampus neurons. Conclusion: GRg1 effectively improves mild cognitive impairment in T2DM rats by inhibiting oxidative stress and reducing the apoptosis of neurons in the cerebral cortex and hippocampus.