Abstract: Objective To analyze the expression and clinicopathologic features of epithelial to mesenchymal transition (EMT) associated protein of cytokeratin-18 (CK-18) and vimentin in gestational trophoblastic disease (GTD).Methods Immunohistochemistry was used to determine theexpression of CK-18 and vimentin in normal pregnancy villis (39 cases), hydatidiform mole (HM) (33 cases) and gestational trophoblastic neoplasia (GTN) (invasive mole 27 cases and choriocarcinoma 5 cases). Results The GTN group had significantly lower levels of CK-18 compared with the normal pregnancy villis group and the HM group (P<0.01). Vimentin was weakly positive in all kinds of trophocyte. There was no significance among normal pregnancy villis,HM and GTN groups (P>0.05). In HM, expression level of CK18 was significantly lower with the increase of the pathological malignancy (P<0.01). And in GTN, the expression of CK-18 was significantly lower with the increase of the tumor anatomy stage (P<0.001). Conclusion The expression of CK-18 decreases with the increase of tropohblast malignancy, which indicates that CK-18 may be involved in malignant transformation of trophocytes and EMT may play an important role in the malignant transformation of GTN.