Background: Increasing evidence has emphasized the important roles of differentially expressed miRNAs in papillary thyroid cancer (PTC) development. miR-199a-5p was previously documented to be down-regulated in PTCs compared with normal thyroids. However, the role of miR-199a-5p in the progression of PTC and the underlying mechanism remain to be further addressed. Methods: miR-199a-5p and SNAI1 family zinc finger 1 (SNAI1) mRNA expressions in PTC tissues and cells were detected by qRT-PCR. The effects of miR-199a-5p and SNAI1 on cell migration, invasion and epithelial-mesenchymal transition (EMT) were evaluated by cell migration and invasion assays, and western blot, respectively. The relationship between miR-199a-5p and SNAI1 was investigated by luciferase reporter assay and western blot. Xenograft tumor assay was performed to verify the role of miR-199a-5p and molecular mechanism in PTC. Results: miR-199a-5p expression was significantly downregulated and SNAI1 was markedly upregulated in PTC tissues and cells. miR-199a-5p overexpression and SNAI1 knockdown suppressed the progression of PTC cells in vitro, as evidenced by the reduced cell migration, invasion and EMT. Of note, SNAI1 was identified as a target of miR-199a-5p and miR-199a-5p suppressed SNAI1 expression in PTC cells. Xenograft tumor assay proved that miR-199a-5p overexpression suppressed tumor growth in PTC in vivo by downregulating SNAI1. Conclusion: miR-199a-5p inhibited the progression of PTC by downregulating SNAI1, offering new insight into the molecular mechanism underlying PTC progression. (C) 2018 Elsevier Inc. All rights reserved.