Abstract: Objective To investigate whether human cervical cancer cell line Siha underwent epithelialmesenchymal transition(EMT) and became more invasive under hypoxia environment, and to explore the underlying molecular mechanism. Methods CoCl₂-treated cells were used to mimic the hypoxia model, then we performed the scratch assay and Transwell migration assays to assess the ability of cell motility, migration and invasion. The expression of EMT markers, E-cadherin and vimentin, as well as hypoxiainducible factor-1α(HIF-1α) were analyzed by immunofluorescence staining and Western blot. qRT-PCR was used to detect the mRNA expression of several EMT-induced transcription factors including snail, zeb and twist. Results Hypoxia microenvironment significantly induced Siha cells motility, migration and invasion properties. The relative expression of E-cadherin in normoxia, hypoxia groups at 12, 24, 48 h were gradually decreased, while that of vimentin was gradually increased. The difference between hypoxia and normoxia groups was significant (P<0.05). HIF-1α expression in Siha cells was up-regulated, and the morphology of Siha cells obviously was transformed and E-cadherin expression was significantly decreased. qRT-PCR demonstrated the relative expression level of twist and snail mRNA were positive correlated with HIF-1α mRNA expression under hypoxia microenvironment, and the difference was significant after 12 h (P<0.01). Conclusion Hypoxia microenvironment could induce EMT and enhance the metastasis of Siha cells through regulating twist and snail and activating HIF-1α.