Abstract: Objective To investigate whether pigment epithelium-derived factor (PEDF) inhibits invasion and metastasis of breast cancer through regulation of epithelial-mesenchymal transition. Methods The expressions of PEDF, vimentin, and E-cadherin were detected in 119 breast cancer tissues using immunohistochemistry. SK-BR-3 breast cancer cell models of PEDF knockdown and PEDF overexpression were established by transfecting the cells with a PEDF-siRNA vector and a lentivirus- PEDF vector, respectively. Western blotting was used to detect the changes in the expressions of PEDF, vimentin, and E-cadherin in the cells, and the cell invasion and migration ability was assessed using scratch wound healing assay and transwell migration assay. Results PEDF positivity rate was significantly lowered in breast cancer tissues compared with the adjacent tissues. PEDF was positively correlated with the tumor size and the expression level of E-cadherin (r=0.473, P<0.001), but was negatively correlated with vimentin expression (r=-0.412, P<0.001). Transwell invasion experiment showed that PEDF interference enhanced the cell invasion and metastasis, while PEDF overexpression inhibited the invasion and migration of SKBR- 3 cells. Western blotting showed that PEDF knockdown significantly decreased the expression of E-cadherin (P<0.05) and increased vimentin expression in the cells (P<0.05). Conclusion PEDF is closely related with the metastasis of breast cancer cells through regulation of epithelial-mesenchymal transition.