Lichen is an association of fungus and alga which intertwined together to form a thallus. The genus Usnea longissima (Parmeliaceae), is a fruticose lichen with numerous biological activities like antimicribiol,antifungal and inhibitory activities for plant and human pathogens. In present work we aimed to reveal the antimicrobial characteristis of some lichens. Taxonomically it is well distinguised by pale greenish to yellowish green colour and pendulous thallus with dense branches usually emerging from the main stem. Its fungal partner releases an extra cellular compound called Usnic acid, a derivative of Dibenzofuran which is a naturally occurring secondary metabolite.