Background: The common treatment for cancer is unfavorable because it causes many detrimental side effects, and lately, there has been a growing resistance toward anticancer drugs, which worsens the future of cancer treatment. Therefore, the focus has now shifted toward natural products, such as spices and plants, among many others, to save the future of cancer treatment. Cloves (Syzygium aromaticum L.) are spices with the highest antioxidant content among natural products. Besides acting as an antioxidant, cloves also possess many other functions, such as anti-inflammatory, antibacterial, and antiseptic, which makes them an ideal natural source to be developed as an anticancer agent. Objective: This study aims to evaluate the cytotoxic activity of cloves toward MCF-7 human breast cancer cell lines. Materials and Methods: Different concentrations of water extract, ethanol extract, and essential oil of cloves were investigated for their anticancer potential in vitro through a brine shrimp lethality test (BSLT) and an MTT assay. Results: In both BSLT and MTT assays, the essential oil showed the highest cytotoxic effect, followed by ethanol and water extract. The LD 50 concentration of essential oil in the 24 hr BSLT was 37 μg/mL. Furthermore, the IC 50 values in the 24 hr and 48 hr MTT assays of the essential oil were 36.43 μg/mL and 17.6 μg/mL, respectively. Conclusion: Cloves are natural products with excellent cytotoxicity toward MCF-7 cells; thus, they are promising sources for the development of anticancer agents.