Many herbs have been discovered to be potential sources of the antitumor and immunomodulatory drug. Areca nut (Areca catechu L.) has a high content of phenols and flavonoids and is highly related to antioxidant activity. Areca nut is a traditional herbal medicine that is popular around Indonesia, India, Thailand, and Taiwan. However, data on its effect on human health showed various results. This chapter’s aim to review the phytochemical and polyphenolic content, the molecular structure of bioactive compounds, the side effect of the crude extract, the role of catechin in cancer mechanism, the antioxidant activity, the cytotoxicity, and immunomodulatory activity of the areca nut. Areca nuts from Aceh province in Indonesia, contain flavonoids, phenolics, catechin, quercetin, and a small percentage of tannins which contribute to antioxidant activity. The areca nut has anticancer potential activity so it can be used in combination with chemotherapeutic agents to enhance the effect at lower doses and thus minimize chemotherapy-induced toxicity. Areca nuts also show immunomodulatory activity which can increase the body’s immune system.