Abstract: Objective To observe the effects of high glucose and/or insulin and metformin intervention on the expression of adenosine monophosphate-activated protein kinasel (AMPK) in breast cancer cells MCF-7, and to investigate the role of AMPK in the occurrence and development of diabetes combined with breast cancer, as well as the mechanism of metformin inhibiting the tumor growth. Methods Western blot and RT-PCR were applied to assess the expressions of AMPK in MCF-7 cells treated with high glucose, high insulin, high glucose plus high insulin and metformin at different concentrations, respectively. Cell cycle was detected by flow cytometry. Results The expression of AMPKα1 and p-AMPK_α1/2 protein in MCF-7 cells treated with high glucose plus high insulin were significantly less than those in control group (P<0.05). In high glucose group, the expression of AMPKα1 protein treated with metformin (5, 10, 20mmol/L) were significantly increased, and the expression of p-AMPK_α1/2 protein and AMPK_α1 mRNA treated with metformin(2.5, 5, 10, 20mmol/L) were also significantly increased, compared with those in control group(P<0.05). In high insulin group, the expression of p-AMPKα1/2 protein and AMPK_α1 mRNA treated with metformin(2.5, 5, 10, 20mmol/L) were significantly increased, and the expression of AMPK_α1 protein treated with metformin (10, 20mmol/L) were significantly increased, compared with those in control group (P<0.05). In glucose plus high insulin group, the expression of p-AMPK_α1/2 protein treated with metformin (5, 10, 20mmol/L) were significantly, and the expression of AMPK_α1 protein treated with metformin (10, 20mM) were significantly increased, moreover, the expression of AMPK_α1 mRNA treated with metformin (2.5, 5, 10, 20mM) were significantly increased, compared with those in control group (P<0.05). Compared with the control group, MCF-7 cells at G1 stage were decreased when treated with high glucose plus high insulin. And metformin-treated (20mM) cells were accumulated at G₁ stage (P<0.05). Conclusion MCF-7 cells cultured with high glucose and high insulin could decrease the expression level of AMPK while metformin could increase the expression of AMPK. High glucose plus high insulin could decrease the MCF-7 cells at G₁ stage, while metformin could block the cells at G₁ stage.