Abstract: Objective To evaluate the effect and mechanism of metformin in promoting the colon cancer cells apoptosis. Methods HCT8 cells were randomly divided into 4 groups,control group,metformin group (5,10 and 20 mM),and the control group did not accept any intervention.Cell proliferation and the inhibition rate of colon cancer cells were identified by MTT methods,apoptosis of colon cancer cells was identified by AnnexinV-FITC cell apoptosis detection kit.Meanwhile,PCR and Western blot was performed to detection mTOR pathways related gene and protein expression respectively. Results Compared with the control group,different concentrations of metformin had inhibitory effect on HCT8,and dose dependently.Twenty mM metformin had the most significant inhibitory effect on colon cancer HCT8 cells,with 5 mM,10 mM and the control group were statistically significant (P<0.05).In addition,with the increase of time,the inhibitory effect of metformin on colon cancer HCT8 increased,72 h inhibition rate with 24 h and 48 h inhibition rate were statistically significant (P<0.05).The results showed that apoptosis rates of 5 mM,10 mM and 20 mM metformin effecting on colon cancer HCT8 cells were (3.16±0.16)%,(5.12±0.39)% and (6.11±0.15)%,respectively,and they were all higher than that of in the control group (1.5±0.28)%,and the differences of apoptosis rate between each group was statistically significant (P<0.05).When treating with metformin,the mRNA and protein expression of 4EBP1,was less than the control group,the difference was statistically significant (P<0.05). Conclusion Metformin inhibits the colon cancer cell proliferation and promote apoptosis of colon cancer cells through inhibiting mTOR signaling pathway.