The anti-metastatic effect of curcumin on papillary thyroid cancer K1 cells and its underlying mechanisms were investigated. Curcumin at 12.5, 25 and 50 μM promoted mesenchymal-epithelial transition and decreased the migration rate of K1 cells by 24-87%. Its mechanism may involve the up-regulation of E-cadherin expression levels and down-regulation of the activity and expression of matrix metalloproteinase-9.