Snail is a master inducer of epithelial-mesenchymal transition (EMT) and metastasis, however, Snail protein is labile and is quickly degraded through the predominate ubiquitination-mediated proteasome pathway. Deubiquitinases (DUBs) can counteract the Snail degradation process to maintain high level of Snail protein in cancer cells. In this study, we screened a cDNA library containing 79 DUBs, and discovered that a panel of DUBs consisting of USP13, USP28, USP29, USP37, OTUD6A, and DUB3 can markedly stabilize Snail protein, with USP29 displaying the strongest activity to prevent Snail degradation. Mechanistically, USP29 enhances the interaction of Snail and SCP1, resulting in simultaneous dephosphorylation and deubiquitination of Snail and thereafter cooperative prevention of Snail degradation. Biologically, ectopic expression of USP29 promotes gastric cancer cell migration, and depletion of Snail abolishes USP29-mediated cell migration; and USP29 can be induced by major EMT and metastatic inducing factors such as TGFβ, TNFα, and hypoxia. More importantly, high expression levels of Snail, USP29, and SCP1 are associated with poor survival and prognosis. Collectively, these data indicate that Snail is a crucial substrate for USP29 to promote cell migration and USP29/SCP1 complex may be new therapeutic targets to treat metastatic cancer.