Objective：This study aims to invesigate the effects of metformin combined pemetrexed on proliferation and apoptosis of human lung adenocarcinoma A549 cells. Methods：The A549 cells were treated with different doses of metformin（0，2.5，5.0，10.0，20.0，40.0 mmol/L）and pemetrexed（0，0.5，1.0，2.0，4.0，8.0 μmol/L）for 48 h，CCK8 assay to assess the antiproliferative of the differently treated A549 cell lines and detect the half maximal inhibitory concentration（IC50）of metformin and pemetrexed；The A549 cells were treated with metformin at IC50，pemetrexed at IC50，and metformin combined pemetrexed to assess the antiproliferative of the differently treated A549 cell lines by the CCK8 assay；The apoptosis of A549 cells was detected by the flow cytometry；The protein expressions of Bcl-2，Bax，Mcl-1 and Noxa were detected by Western blot. Results：The proliferation of A549 cells was inhibited by metformin and pemetrexed monotherapy in a dose-dependent manner compared with the control groups（P < 0.05）；The combination of metformin and pemetrexed induced higher percentage of cell proliferation than that of metformin and pemetrexed used alone（P < 0.05）in a time-dependent manner（P < 0.05）；Apoptosis rate of metformin combining pemetrexed［（30.6 ± 0.4）%］was significantly higher than that of metformin［（13.3 ± 0.3）%］ and pemetrexed［（12.9 ± 0.1）%］group，respectively（P < 0.05），The combination of metformin and pemetrexed down regulated the protein expression of Bcl-2 and Mcl-1，up-regulated the protein expression of Bax and Noxa compared with metformin and pemetrexed monotherapy. Conclusion：metformin combined with pemetrexed can inhibit in vitro human lung adenocarcinoma A549 cells proliferation and apoptosis，the mechanism may be connected with down-regulation of Bcl-2 and Mcl-1，up-regulation of Bax and Noxa expression.