In the present investigation, a total of thirty two endophytic diazotrophs were isolated from rhizosphere weedy grasses of different physiographic regions of southern India. Among the diazotrophic isolates seven were screened by nitrogenase activity and higher activity of 166.25 ±13.95 n moles ethylene/mg protein /h exhibited by the isolate Bacillus sp.CBE9. All but one recorded the presence of nif gene by PCR using universal primers. The 16S rRNA gene sequence homology revealed the presence of diversity of g Proteobacteria and Firmicutes. Plant growth promoting traits of all the selected diazotrophic isolates were analysed and results revealed that diazotrophs were found to produce phytohormone, siderophores, HCN, solubilize minerals such as P, K, Zn and synthesize enzymes such as ACC deaminase that can modulate plant growth and development. Additionally, diazotrophic strains showed tolerance to various abiotic stresses such as heavy metals, salt, temperature and drought. In the plant inoculation study, the dehulled and surface sterilized seeds treated with diverse diazotrophic strains showed a 41% and 58% increase in root length as well as shoot length respectively when compare with control.  The endophytic colonization in the rice seedlings (roots and culm) were examined by SEM analysis. Results indicated that endophytic bacteria were preferentially colonized in the rhizoplane and inner side of rice roots.