Allium sativum L (garlic) has a lengthy history as being a food and spice having a unique taste and odor along with many medicinal properties. Garlic is considered to be a natural medicine against variety of human ailments, including various antibacterial, antiviral and antifungal infections, antithrombotic, anticancer and anti tumorogenic activities. All these activities are linked to the level of organosulfur compounds like allicin, flavonoids, and phenolic components in it. Freshly chopped garlic contains Allicin, which is one of the highly biologically dynamic component. Allicin has reported to have a number of bioactivities including antioxidant, antiinflammatory activities. Many cardiovascular activities of allicin also have been worked out. The present paper reviews one of the major active ingredients in garlic – allicin – for its medicinal importance.