Garlic(Allium sativum L.) is one of the oldest cultivated plants and has been used throughout the world as food supplement and folk medicine for thousands of years. In modem times a number of garlic derived products are introduced on the market as health food supplement in ever growing scale. In 1844 German chemist Wertheim investigated the garlic first time chemically and thereafter many kinds of organosulfur compounds were isolated and their biological activities were elucidated scientifically. The main biological activities are antibacterial, antifungal, antithrombotic, cholesterol-lowering, antineoplastic and hepatoprotective activities. Chemical works as well as therapeutic and preventive effects of garlic are reviewed.