Objective:To elucidate the function of melatonin on hypoxia -induced epithelial- mesenchymal transition (EMT) of SGC-7901 gastric cancer cells and to reveal the mechanisms underlying. Methods:After hypoxia for 96h,expression of epithelial and mesenchymal makers of SGC-7901 gastric cancer cells was detected using Western blot and immunofluorescence was employed to investigate distribution of proteins to see if EMT acured. Then we treated SGC-7901 gastric cancer cells by 1 mmol/L concentration of melatonin under hypoxia environment to see if EMT was inhibited. Results:Hypoxia induced morphological change of SGC-7901 gastric cancer cells,as well as decreased E-cadherin and increased vimnetin and α-SMA. The reactive oxygen species ( ROS) and exprssion of hypoxia-inducible factor-1α(HIF-1α) both abolished by treatment of melatonin,so as EMT. Conclusion:We found that melatonin can abolish hypoxia-induced EMT of SGC-7901 gastric cancer cells,which can be used for clinical application.