Abstract: Plants of leguminous family are associated specifically with Rhizobium sp. which plays a crucial role in agriculture, forestry and nutrient cycling by maintaining soil fertility through biological nitrogen fixation.The Rhizobia includes genus Rhizobium, Mesorhizobium, Bradyrhizobium, Ensifer and Azorhizobium belongs to α proteobacteria.Despite the high specificity between Rhizobium and legumes, the presence of non-rhizobia in root nodules has been reported.These are belonging to α, β and δ-Proteobacteria.This review through a light on diversity and role of these non-rhizoidal species in their host.