Tetrandrine (TET), a bisbenzylisoquinoline alkaloid found in traditional Chinese medicines, exerts anticancer activity in vitro and in vivo. However, its potential role in the prostate cancer metastatic process has not yet been elucidated. Thus, we investigated the inhibition effect of tetrandrine on prostate cancer migration and invasion and the corresponding molecular basis underlying its anticancer activity. Cell migration and invasion were determined using the Transwell chamber model. The protein expression of Akt, phosphorylated Akt, the mammalian target of rapamycin (mTOR), phosphorylated mTOR and matrix metalloproteinases 9 (MMP-9) was detected by western blot in the presence or absence of tetrandrine or in the group tetrandrine combination with LY294002 (inhibitor of Akt) and rapamycin (inhibitor of mTOR). Our studies showed that excluding the effect of tetrandrine on cell proliferation, tetrandrine significantly inhibited cell migration and invasion in prostate cancer DU145 and PC3 cells. Furthermore, tetrandrine decreased the protein levels of p-Akt, p-mTOR, and MMP-9. While the inhibition of Akt or mTOR by the respective inhibitors could potentiate this effect of tetrandrine on prostate cancer cells, the studies indicate that tetrandrine inhibits the metastasis process by negatively regulating the Akt/mTOR/MMP-9 signaling pathway. These results suggest that tetrandrine might serve as a potential metastasis suppressor to treat cancer cells that have escaped surgical removal or that have disseminated widely.