The use of medicinal plant to healing is the alternative medicine that can improve the quality of the patient’s life and less side effect. Clove (Syzygium aromaticum (L) Merr.& Perry) is one of thai herb that has eugenol as main organic compound. Eugenol possesses pharmacological activities including antiseptic and antibiotic activity. There also found that eugenol can inhibit proliferation of cancerous cell. This research is aim to study effect of eugenol on human breast cancer cell line, MCF-7. The cells were exposed to three concentration (1 μM ,2.5 μM and 5 μM) of eugenol compared with the effect of anticancer drug, Etoposide. Mitotic index and viability were used to evaluate cytotoxic effect. It was found that eugenol can decrease viability and mitotic index of breast cancer cell line, MCF-7.