Nitrogen fixation in faba beans is associated with nodule bacteria Rizobium leguminosarum.  In this study, hydrogen uptake activity was well distributed in Rhizobium leguminosarum isolated from nodules of faba bean (Vicia faba).  Two Rhizobia effective strains namely, ICARDA 441 and ARC 207, exhibiting significantly higher hydrogen uptake activity were subjected to mutagensis with nitrosoguanidine.  The respective mutation frequencies were 0.20 and 0.22%.  Three negative Hup mutants each of ICARDA 441 and ARC 207 were compared parental with the wild type strains under pot experiments to evaluate the significance of the hydrogen uptake system in biological nitrogen fixation .The all parameters tested, nodulation statues, plant growth characteristics, nitrogenase activity and nitrogen content were significantly reduced in the plants treated with negative hydrogen uptake mutants strains.