MicroRNAs (miRNAs) play critical roles in the development and progression in various cancers.Dysfunctional miR-9 expression remains ambiguous,and no consensus on the metastatic progression of ovarian cancer has been reached.In this study,results from the bioinformatics analysis show that the 3’-UTR of the E-cadherin mRNA was directly regulated by miR-9.Luciferase reporter assay results confirmed that miR-9 could directly target this 3’-UTR.miR-9 and E-cadherin expression in ovarian cancer tissue was quantified by qRTPCR.Migration and invasion were detected by wound healing and Transwell system assay in SKOV3 and A2780.qRT-PCR and West blot were performed to detect the epithelial-mesenchymal transition-associated mRNA and proteins.Immunofluorescence technique was used to analyze the expression and subcellular localization of Ecadherin,N-cadherin,and vimentin.The results showed that miR-9 was frequently upregulated in metastatic serous ovarian cancer tissue compared with paired primary ones.Upregulation of miR-9 could downregulate the expression of E-cadherin but upregulate the expression of mesenchymal markers (N-cadherin and vimentin).Overexpression of miR-9 could promote the cell migration and invasion in ovarian cancer,and these processes could be effectively inhibited via miR-9 inhibitor.Thus,our study demonstrates that miR-9 may promote ovarian cancer metastasis via targeting E-cadherin and a novel potential therapeutic approach to control metastasis of ovarian cancer.