Background and Aim: Breast cancer is the second leading cause of death among women worldwide. Despite recent advances in cancer treatment, this disease remains one of the leading causes of death. Snake venom is a mixture of various molecules such as carbohydrates, nucleosides, amino acids, lipids, proteins and peptides. Previous studies have shown that the venom of some snakes have anti-cancer effects on human cell lines. In the present study, the effect of Vipera raddei kurdistanica venom on breast cell lines was investigated. Materials and Methods: The effect of increasing concentrations of snake venom on breast cells viability was investigated using 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide assay and lactate dehydrogenase measurement. Apoptotic cell death was evaluated by fluorescent dye staining and DNA fragmentation assay. Changes in the expression levels of some apoptotic-related genes were investigated by using real time PCR. Data were analyzed by one-way ANOVA followed by Tukey's test. P