Wnt/β-catenin signaling plays a role in tumorigenesis of human papillary thyroid cancer (PTC). Dickkopf-1 (Dkk-1) is an inhibitor of Wnt/β-catenin signaling. We investigated the therapeutic potential of Dkk-1 in human PTC cell lines, SNU-790, B-CPAP, and BHP10-3. Dkk-1 reversed the aberrant expression of β-catenin from nucleus to membrane and inhibited basal levels of TCF/LEF-dependent transcriptional activities. Furthermore, Dkk-1 inhibited cell viability in a dose-dependent manner and adenoviral transduction of constitutively active β-catenin blocked these effects, thus suggesting that the Dkk-1 anti-tumoral effect is mediated by Wnt/β-catenin signaling. Bromodeoxyuridine assay showed minimal effects of Dkk-1 on cell proliferation. Flow cytometric analysis with Annexin V staining showed marked induction of cell apoptosis by Dkk-1 treatment. Dkk-1 also restored the loss of membranous E-cadherin expression with consequent inhibition of cell migration and invasion. In conclusion, Dkk-1 inhibited the survival and migration of human PTC cells by regulating Wnt/β-catenin signaling and E-cadherin expression.