Recently, the scientific community has begun to establish the health benefits of deep-sea water (DSW) due to its enrichment in nutrients and minerals. In this study, we investigated the effects of deep-sea water (DSW) on the metastatic potential of two human breast cancer cell lines exhibiting highly different phenotypes. MDA-MB-231 cells exhibit invasive/metastatic tumor features with rapid migration ability and high endogenous expression of TGF-β and Wnt5a. DSW treatment significantly inhibits their migratory ability in a wound-healing assay. This inhibitory effect of DSW appears to be mediated through TGF-β and Wnt5a signaling, resulting in attenuated expression of CD44. We further investigated the preventive effect of DSW on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced invasive/metastatic tumor features in non-invasive MCF-7 cells. Similar to the inhibitory effects shown in MDA-MB-231 cells, we observed that DSW treatment resulted in the inhibition of TPA-induced migration and MMP-9 activity with a concomitant decrease in mRNA levels of MMP-9, TGF-β, Wnt5a and Wnt3a. Taken together, our data show that DSW has inhibitory effects on breast cancer invasion/metastasis, suggesting that DSW has some promise in improving cancer survival by preventing tumor metastasis.