Epithelial-mesenchymal transition (EMT) is regarded as the most important mechanism behind the initiation of cancer metastasis. Though there has been great interest in developing therapies aimed at impairing the process of EMT, only few molecules have been identified to orchestrate it so far. Here we report that the dual PI3K/mTOR inhibitor NVP-BEZ235 is capable of preventing human ovarian cancer cell line SKOV-3 and prostatic cancer cell line PC-3 from hypoxia- and TGF-β1-induced EMT. The addition of NVP-BEZ235 reverses the EMT-like morphologic changes, down-regulation of E-cadherin, and enhancement of cell migration induced by 1% O2 partially through interfering with the expression and transcriptional activity of Hif-1α via PI3K/mTOR pathway. In addition, NVP-BEZ235 inhibits TGF-β1-induced phosphorylation of Smad2/3 and Akt/GSK-3β, reduces the expression of Snail both in transcriptional and post-translational level, and consequently prevents the repression of E-cadherin expression as well as the increase of cell motility caused by TGF-β1. Moreover, in nude mice bearing SKOV-3 ovarian cancer xenografts, NVP-BEZ235 significantly increases the mRNA level of E-cadherin. Taken together, our study demonstrates, for the first time, NVP-BEZ235 can prevent microenvironment and growth factor induced EMT, which suggests this agent as a potential candidate for cancer metastasis treatment.