Objective：To observe effects of metformin on proliferation and related gene expression of human pancreatic cancer cell line Patu8988 treated by diabetic serum.Methods：Patu8988 cells were cultured with diabetic serum，or healthy human serum as control.The two groups were treated with different concentrations of metformin (2.5，5.0，10.0，20.0，and 40.0 mmol/L.The proliferation was measured by cell counting kit-8 (CCK-8) assay，and the expressions of matrix metalloproteinase-2 (MMP-2)，matrix metalloproteinase-8 (MMP-8) and matrix metalloproteinase-11 (MMP-11) were examined by real-time PCR.Results：Compared with the control group，the proliferation of Patu8988 was promoted after treatment with diabetic serum (0.74±0.03 vs.0.62±0.02，P＜0.01)：Metformin inhibited the proliferation of Patu8988 treated with diabetic serum (P＜0.01)，and the expressions of MMP-2，MMP-8 and MMP-11 were downregulated.Conclusion：Metformin inhibits the proliferation of cancer cells induced by the serum from patients with diabetes，which may be related to the down regulation of MMP-2，MMP-8, and MMP-11.