Olive oil is one of the most common and important cooking oils is obtained from olive fruits. It is known as the main source of bioactive phenyl ethyl alcohol, hydroxytyrosol. Hydroxytyrosol and its derivatives representing half of the polyphenols occurring in olive oil and are responsible for the nutraceutical properties and pharmacological effects of olive oil. Hydroxytyrosol is easily absorbed and it has a good bioavailability. In addition, hydroxytyrosol has negligible adverse effects and therefore, much attention has been paid to this compound as one of the most important polyphenols. Up to now, several scientific reports demonstrated a wide range of pharmacological effects about hydroxytyrosol. Therefore, the present study aimed to critically review the available knowledge about health-promotion effects of hydroxytyrosol and its chemistry, bioavailability, pharmacokinetics and toxicity. Keywords: Antioxidant, cardioprotective, hydroxytyrosol, olive oil, polyphenols.