In this study, we examined serum miR-21 levels in epithelial ovarian cancer (EOC) patients, and explored its association with clinicopathological factors and prognosis. The results showed significantly higher serum miR-21 levels in EOC patients than in healthy controls. In addition, increased serum miR-21 expression was correlated with advanced FIGO stage, high tumor grade, and shortened overall survival. These findings indicate that serum miR-21 may serve as a novel diagnostic and prognostic marker, and be used as a therapeutic target for the treatment of EOC