MicroRNA-145 (miR-145) expression is downregulated in several human cancers, but its clinical and functional relevance to ovarian carcinoma has not yet been elucidated. This study addressed the hypothesis that miR-145 serves as a prognostic biomarker and a tumor suppressor that regulates the expression of high-mobility group A2 (HMGA2) oncoprotein in ovarian cancer. Here, we found that low miR-145 expression and HMGA2 overexpression determined by qRT-PCR and immunohistochemistry significantly correlated with advanced stage, lymph node involvement, and distant metastasis in 74 ovarian carcinomas. Low miR-145 expression significantly correlated with tumor recurrence and worse overall survival (HR=8.62, P = 0.039). Transfection of pre-miR-145 resulted in reduced cell growth and migration, and increased apoptosis of ovarian cancer cells by TUNEL, colony forming, and cell migration assays. MiR-145 was found to directly target HMGA2 by luciferase assay and Western blotting. Our findings suggest that miR-145 functions as a tumor suppressor in ovarian cancer and directly targets HMGA2 oncoprotein. Low miR-145 and high HMGA2 expressions are potential biomarkers of poor prognosis of ovarian carcinoma and miR-145 is the more powerful predictor of patient outcome.