Objective: To investigate the role of mammalian target of rapamycin (mTOR) in human granulosa cell ovarian tumors and the therapeutic effectof rapamycin in COV434 mitotic granulosa cell lines.Material and Methods: A retrospective evaluation of the medical records and pathologic sections of patients with granulosa cell ovariancarcinoma was performed. mTOR and p-mTOR expression was immunohistochemically investigated. A COV434 cell culture were treated with0.5, 1, 2, and 5 μM rapamycin. Real-time growth curve analysis via xCELLigence system and apoptotic cell analysis via YO-PRO™-1 Iodide wereperformed to assess the therapeutic effect of rapamycin on cancer cells.Results: A total of twenty patients were evaluated. mTOR staining was detected in 18 (90%) patients. Mild, moderate, intense, and very intensestaining was observed in three (15%), eight (40%), six (30%), and one (5%) sample, respectively. The mean mTOR staining ratio was 59±41%.P-mTOR staining was observed in two (10%) patients. One (5%) patient had 5% staining, and one (5%) patient had 100% staining for p-mTOR.Both of the latter patients had very intense staining. Rapamycin caused a dose-dependent growth arrest and induced apoptosis in COV434 mitoticgranulosa cells. The real-time growth curves of the cells treated with these drugs were distinguished by a marked reduced slope after exposurefor several hours, indicating a rapid onset of apoptosis. Live/dead cell analysis with YO-PRO-1 staining showed that rapamycin induced apoptosisin 24% of the cells when used at 1 μM concentration, whereas the rate increased to 61% and 72% when the cells were treated with 2 μM and 5μM rapamycin, respectively.Conclusion: mTOR expression is observed in various degrees in 90%, and p-mTOR expression is observed in only 10% of patients with granulosacell ovarian carcinoma. Rapamycin caused a dose-dependent growth arrest and apoptosis in COV434 mitotic granulosa cells.