This work aims to investigate the antiproliferative properties of Allium sivasicum (AS) on breast cancer. AS extracts were studied for cytotoxicity against the breast cancer cell lines. In vitro apoptosis studies of breast cancer cells were performed by annexin V staining in flow cytometry analyses. AS showed cytotoxicity to three cancer cell lines. Annexin-positive cells level in AS treated cell lines were higher than the untreated control cells. The expressions of caspase-7 protein and TUNEL positive cells were much higher for the rats treated by AS, compared with the untreated control group. The expressions of the Ki-67 decreased in treatment groups compared with the control group. In vivo studies showed that mean tumor volume inhibition ratio in AS treated group was 38 % compared with the untreated rats. These results indicate that A. sivasicum has antitumoral potential against breast cancer.