Abstract: Objective To determine the potential role of miRNAs in controlling EMT and metastasis in ovarian cancer cells. Methods Firstly, we used 2 computational algorithms, TargetScan and PicTar, to search for miRNAs that could target 3' UTR of CDH1 mRNA. Luciferase reporter assay, qRT- PCR and Western blot were carried out to validate the results. Immunofl uorescence staining of E-cadherin, ?-Catenin and Vimentin were performed to detect the EMT process of ovarian cancer cell lines transfected with miRNAs. Wound healing assay and Transwell assay were used to detect the cell motility and invasiveness. Results miR-9 directly regulated CDH1, causing a remarkable inhibition of E-cadherin expression. miR-9 also caused a dramatic increasing of ß-Catenin and Vimentin expression, which were the important molecular markers of EMT process. Moreover, up-regulation of miR-9 in ovarian cancer cell lines signifi cantly improved cell motility and invasiveness. Conclusion miR-9 has a significantly promoting effect on EMT via directly targeting E-cadherin in ovarian cancer cells, and may play a potential important role in cancer metastasis and invasiveness.