Abstract: Objective :To investigate the amplification and protein expression of AIB1 gene, aswell as its clinical significance, in ovarian cancer. Methods :Fluorescence In Situ Hybridization (FISH),immunohistochemistry and flow cytometry methods were used to detect the amplification and expressionof AIB1 gene and DNA ploidy in ovarian cancer, so as to analyze their correlations and association withpatient's clinical features. Results :Of the 80 ovarian cancers in the study, the over-expression of AIB1protein in 28 (38%) were observed. There was a significant association between AIB1 expression andtumor's Silverberg grade and FIGO stage (P<0.05), where the over-expression of AIB1 in 44% tumorswith Silverberg grade 2-3 and 46% cases in FIGO stage III-IV were observed, which was significantlymore frequent than that in tumors with Silverberg grade 1 (13%) and FIGO stage I-II (14%). In FISHstudy of the ovarian cancer group, only 9% cases were detected in amplification of AIB1 gene. In addi-tion, an anupolid DNA content in 89% cases of ovarian cancer with the over-expression of AIB1 wereobserved. Conclusions :The over-expression of AIB1 protein in ovarian cancer is closely associatedwith tumor's pathological grade, clinical stage and chromosomal instability. In regulation of AIB1 pro-tein expression, there might exist mechanism other than AIB1gene amplification.