ABSTRACT This paper aims to clarify the effect of Undercarboxylated osteocalcin (ucOC) on cognitive function in rats with type 2 diabetes mellitus (T2DM). This research reviewed the cognitive function of 35 diabetic patients, 33 non-diabetic patients and the serum levels of Undercarboxylated osteocalcin (ucOC) in patients. What’s more, we analyzed the correlation between serum ucOC levels and cognitive function. Diabetic rats were treated with high (30 μg·kg−1·d−1) and low (10 μg·kg−1·d−1) doses of ucOC to investigate its effects in regulating ucOC on blood lipid, blood glucose and cognitive function. We systematically detected the phosphorylation levels of cognitive level-related proteins (PI3K, AKT, and GSK/3β) in the hippocampus by Western Blot. Finally, PI3K-Akt pathway involved in regulating cognitive function in diabetic rats by ucOC was verified with AKT pathway inhibitor LY294002. MoCA score and serum ucOC levels were significantly reduced in patients with diabetes mellitus. ucOC could concentration-dose-dependently decrease the blood glucose and lipid levels, and improve glucose metabolism and weaken insulin resistance in diabetic rats (P < 0.001). In addition, escape latency in diabetic rats was significantly higher than that of normal rats in the Morris maze test, and ucOC dose-dependently shortened the escape latency in diabetic rats (all with P < 0.05). After using AKT pathway inhibitor, ucOC failed to shorten the escape latency in diabetic rats. In conclusion, this study explored the relevant mechanisms in inducing cognitive dysfunction of T2DM, suggesting the potential value of ucOC as a drug to improve cognitive dysfunction in patients with T2DM in clinical.