Mesenchymal stem cells (MSCs) have surfaced as ideal candidates for treatment of different therapeutically challenging diseases however their effect on cancer cells is not well determined. In this study, we investigated the effect of MSCs derived from human bone marrow (BM), adipose tissue (AT), and umbilical cord derived MSCs (UC-MSCs) on ovarian cancer. Measurements of ovarian tumor marker proteins were computed by ELISA. Proliferative, apoptosis and anti-inflammatory effects of the MSCs were measured by Flow cytometry (FCM). MMPs expression was measured by RT-PCR. The co-culture of cancer cell lines OVCAR3, CAOV3, IGROV3 and SKOV3 with the conditioned media of MSCs (CM-MSC) and MSCs showed an increase in cellular apoptosis, along with a reduction in the level of CA-125 and a decline of LDH and beta-hCG. A decrease in CD24 of the cancer cell lines in co-culture with the CM-MSCs showed a reduction of the cancer tumorigenicity. In addition, the invasion and aggressiveness of cancer cell lines was significantly decreased by CM-MSC; this was translated by a decrease in MMP-2, MMP-9, and CA-125 mRNA expression, and an increase in TIMP 1, 2, and 3 mRNA expression. An increase in IL-4 and IL-10 cytokines, and a decrease in GM-CSF, IL-6, and IL-9, were also noted. In conclusion, mesenchymal stem cells derived from different sources and their conditioned media appear to have a major role in inhibition of cancer aggressiveness and might be considered as a potential therapeutic tool in ovarian cancer.