The use of biofertilizers has become a great hope for Egyptian agriculture, particularly in the field of production of medicinal plants, especially when the economic and environmental points of view are considered, since they reduce the environmental pollution and production costs, in addition to improving the quality. Therefore, the influence of using locally isolated nitrogen fixing bacteria as biofertilizers were studied. The isolates used were three representative strains of either Azotobacter and Azospirillum (two isolates of Azotobacter out of 60 isolates, these isolates were Az.NP7- Az.PR1, and one isolate of Azospirillum out of 60 isolates, this isolate was As.Pp1 ) which were screened for their activity in nitrogen fixing and stimulation effect by used root exudates of black-cumin plants and used for further inoculation studies as biofertilizers. These isolates were isolated at random from rhizosphere and rhizoplane of black-cumin, parsleyand fenugreekcultivars at the different stages of growth. The effect of inoculation with N₂-fixing bacteria ( biofertilizer ) on growth plant characteristics of tested medicinal  plants ( Nigella sativa, Trigonella foenum- graecum and Petroselinum sativum) plants were studied. Inoculation was conjugated with the application of four doses of mineral N, i.e. 0, 50%, 75% and one full dose ( 100% ) from the recommended doses. Results obtained showed that the application of biofertilizers ( N₂-fixers ) produced better growth and reduced the N requirement in many medicinal plants such as Nigella sativa, Trigonella foenum and Petroselinum sativum compared with untreated plants.