Tuberculosis (TB) is the main cause of morbidity in modern era and a latent infection affecting nearly one third of world’s population including forty percent from India. There is an urgent need to explore the effective and promising new anti– tubercular drugs to combat against Tuberculosis. Nature provides diverse secondary metabolites with anti- tubercular activity in medicinal plants. Among them Allium cepa (onion)., contains various constituents like quercetin, fructose, quercetin-3-glucoside, isorhamnetin-4-glucoside, xylose, galactose, glucose, mannose, organosulfur compounds, allylsulfides, flavonoids, flavenols, S-alk(en)yl cysteine sulfoxides, cycloalliin, selenium, thiosulfinates, and sulfur and seleno compounds that have proved to have protective role in tuberculosis. Allium cepa (onion) possesses antibiotic activity against both Gram-positive and Gram-negative bacteria and can be used to prevent tuberculosis most effectively.