Background: Zerumbone is a sesquiterpene which was found to delay progression of breast cancer through apoptosis induction via up-regulating Bax protein and down-regulating Bcl2 protein. Purpose: In this study, we aimed to investigate Zerumbone, a natural compound of medicinal herbal plant isolated from Zingiber zerumbet, for anti-cancer activity against MCF-7 cell line. Methods: Human cancer cell lines of breast MCF-7 cells were obtained from American Type Culture Collection (ATCC, Manassas, VA). ON target plus smart pool siRNA, the most efficient method is used for preparation of β-catenin siRNA. Cyclophilin B siRNA is considered as positive control. Zrumbone is an ethanol-soluble compound isolated from Zingiber zerumbet, extracted by the hydro-distillation (steam distillation) method. Purification of ZER was examined using HPLC. The MCF-7 cells transfected with 100 µM human β-catenin (CTNNB1) siRNA or cyclophilin B siRNA positive control. After transfection, the cells were harvested at 48hrs for mRNA analysis or 48 – 72 hrs for protein analysis. IC50 for ZER was determined using MTT assay. MCF-7 transfected with β-catenin siRNA were then treated with ZER IC50. The mRNA expression was analyzed using real-time to ensure the knock down of β-catenin. TUNNEL assay was used to confirm apoptosis and flow cytometry was applied for quantification of apoptotic cells. Western blot analysis was done to evaluate the effect of ZER and β-catenin (CTNNB1) siRNA on the expression of β-catenin and its functional impact on the proliferation and survival of MCF-7 cells. Results: ZER decreased β-catenin protein expression in breast cancer cell lines. ZER downregulated β-catenin mRNA level in breast cancer cell lines. Depletion of β-catenin by β-catenin siRNA and ZER induce cell apoptosis. Apoptosis caused by ZER was confirmed/examined using by annexin V (annexin V was used as a marker for drug action). Conclusion: Zerumbone possesses anti-breast cancer activity, which could be attributed to the reduction of β-catenin protein expression in MCF-7 breast cancer cell lines, downregulation of β-catenin mRNA level in breast cancer cell lines and through annexin V.