Summary: In order to explore a potential indicator of predicting the occurrence and development of gestational trophoblastic tumor, the expression of c-erbB2 oncogene in human normal placenta, hyda tidiform mole and choriocarcinoma was investigated. The expression of c-erbB2 was detected im munohistochemically by monoclonal antibody against the gene on the formalin-fixed paraffin sections of 21 hydatidiform moles, 21 invasive moles, 20 choriocarcinomas and 30 normal placentas. Results showed that the expression level of c-erbB2 was significantly higher in gestational trophoblastic tumor than in hydatidiform mole and normal placenta of midterm and term pregnancy (P＜0. 05), while there was no significant difference between patients with gestational trophoblastic tumor of stage Ⅲ ,Ⅳ and those of stage Ⅰ , Ⅱ . It was demonstrated that overexpression of c-erbB2 may closely associ ated with malignant transformation of hydatidiform mole, not only providing important insight into pathogenesis of gestational trophoblastic tumor, but also having an important significance for the ear-ly diagnosis and early treatment of gestational trophoblastic tumor.