Abstract Over the decades, the increased interest in the use of natural resources in pharmaceutical and phytotherapeutic research has led to manufacture of drugs (including anti-cancer drugs) derived from natural sources With our increased understanding of the molecular mechanisms underlying cancer progression and cell death, it is therefore necessary to test if there are any natural products that can be used to act as antitumor agents. As breast cancer continues to be the leading cause of cancer in females, we aimed to exploit the use of South African traditional medicine, Euphorbia mauritanica as a tool for anti breast cancer therapy. Euphorbia mauritanica was tested for anti-proliferative properties against MCF-7 and Cama-1 breast cancer cell lines. The following solvents were used to extract active compounds from E. mauritanica: n-hexane, dichloromethane, chloroform, ethyl acetate, acetone, methanol and butanol. A real time cell analyzer (Xcelligence) was used to monitor cell growth over a period of 48 hours following treatment of cells with the extracts. Butanolic extracts showed the highest level of cytotoxicity on both MCF-7 and Cama-1 cell lines with IC50 of 15 and 30 µg/ml respectively. These were followed by hexanolic extracts with IC50 of 30 and 50 µg/ml and methanolic extracts with IC50 of 50 and 100 µg/ml. Flow cytometry using annexin V was further employed to determine if cell death was as a result of apoptosis and the data confirmed that this was most likely the case. On investigating whether the observed apoptosis was via p53 mediated pathway, western blot analysis of p53, bcl-2, caspase 9, caspase3, RBBP6 and mdm2 showed that treatment with the 3 extracts did not have a significant effect on any of these genes, suggesting that their mode of apoptosis induction maybe through an alternative apoptotic pathway. Citation Format: Mpho S. Choene, Lesetja R. Motadi. Anti-proliferative properties of Euphorbia mauritanica medicinal plant against breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3216. doi:10.1158/1538-7445.AM2014-3216