Abstract: Objective : To evaluate the clinical significance of platelet count in epithelial ovarian cancer, and to investigate the correlation between an increase in platelet count and the incidence of epithelial ovarian cancer. Methods : Platelet count and pre- and post-operative CA125 were compared among three groups: the earlystage epithelial ovarian cancer group (n=80), the advanced stage epithelial ovarian cancer group (n=50) andthe benign ovarian tumor group (n=90). All patients were randomly recruited for the study between January2002 and July 2007. Results : The mean platelet count was 234.55±71.51 (×10⁹/L) in the early stage epithelialovarian cancer group, 308.12 ± 111.95 (× 10⁹/L) in the advanced stage epithelial ovarian cancer group, and 206.28±52.62 (×10⁹/L) in the benign ovarian tumor group, with a significant difference among the 3 groups (P<0.05). There was a correlation between thrombocytosis and the incidence of residual tumor when the originaltumor diameter was greater than 2 cm. In general the platelet count was decreased after surgery. In the earlystage epithelial ovarian cancer group, the platelet count was correlated with histopathology. In the advancedstage epithelial ovarian cancer group, however, no correlation was found between platelet count andhistopathology, CA125, abdominal edema, or lymph node metastasis. Conclusion : An increased platelet countis commonly seen in patients with epithelial ovarian cancer, but it usually decreases after surgery. Patientswith thrombocytosis have a poor prognosis. Platelet count has no correlation with CA125, but it can be usedas a marker for the development and prognosis of epithelial ovarian cancer.