Abstract: Objective: To investigate the role of mutation and mRNA expression of tumor suppressor gene PTEN in tumorigenesis and progression of ovarian cancer. Methods: Mutated exon 5 of PTENgene was detected in normal ovary (n=5), epithelia ovarian cyst (n=5), epithelia ovarian borderline tumor (n=9), ovarian cancer (n=60) by PCR-SSCP. mRNA expression of PTEN gene was evaluated in cor-responding tissues by RT-PCR. The mutation or mRNA expression of PTEN gene was compared with clinicopathological features of ovarian cancer. Results: Mutated exon 5 of PTEN gene was examined only in 5 (7.1%) cases of epithelium-derived ovarian cancer. mRNA expression level of PTEN gene was lower in ovarian borderline tumor and ovarian cancer than that in normal ovary and ovarian cyst (P <0.05). mRNA expression level of PTEN gene was negatively correlated with clinicopathological staging,but positively with histological differentiation (P < 0.05). mRNA expression level of PTEN gene was thelowest in ovarian endometrioid cancer, significantly lower than ovarian serous and mucinous cancer (P <0.05). Conclusions: Mutated exon 5 and reduced mRNA expression of PTEN gene occurred in ovariancancer. Down -regulated mRNA expression of PTEN gene was closely associated with pathobiological behavior of epithelial ovarian cancer, specially of ovarian endometrioid cancer. Thus, PTEN gene might be a pathobiological molecular marker oi ovarian cancer.