Abstract: This study is to evaluate the effects of the metformin(Met)on β cell function of diabetic KKAy mice. Female diabetic KKAy mice selected by insulin tolerance test(ITT)were divided randomly into two groups. Con group was orally administered by gavage with water, Met group with metformin hydrochloride at a dose of 0.2 g·kg^-1 for about 12 weeks. ITT and glucose tolerance tests(OGTT)were determined. Beta cell function was assessed by hyperglycemic clamp. Pancreatic biochemical indicators were tested. The changes of gene and protein expression in the pancreas and islets were also analyzed by Real-Time-PCR and immunostaining. Met significantly improved glucose intolerance and insulin resistance in KKAy mice. Fasting plasma glucose and insulin levels were also decreased. In addition, Met markedly increased glucose infusion rate(GIR)and elevated the I^st phase and maximum insulin secretion during clamp. It showed that Met decreased TG content and iNOS activities and increased Ca²⁺-Mg²⁺-ATPase activity in pancreas. Islets periphery was improved, and down-regulation of glucagon and up-regulated insulin protein expressions were found after Met treatment. Pancreatic mRNA expressions of inflammation factors including TLR4, NF-κB, JNK, IL-6 and TNF-α were down-regulated, p-NF-κB p65 protein levels also down-regulated by Met. And mRNA expressions of ion homeostasis involved in insulin secretion including SERCA2 and Kir6.2 were up-regulated by Met. Met increased SIRT5 expression level in pancreas of KKAy mice under the hyperglycemic clamp. These results indicated that chronic administration of Met regulated pancreatic inflammation generation, ion and hormone homeostasis and improved β cell function of diabetic KKAy mice.