A total of 18 bacterial strains were tested for IAA production using colorimetric method. Tryptic soy broth with and without were used as IAA production media. Among these, only Enterobacter asburiae produced the significant amounts of IAA (18.9 um) when tryptophan was not added to the growth medium as the precursor of IAA biosynthesis (table2). The others strains produced IAA in this medium less than 10 uM. However, most strains produced higher amounts of IAA in the presence of tryptophan in the medium. E. asburiae released the highest amount of IAA (19.8 uM) in the media containing 600 ug/ml of tryptophan. Furthermore, the effect of tryptophane concentration on IAA production of E. asburiae was investigated. It was found that IAA production of E. asburiae did not significantly increase with an increase in the concentration of tryptophan. However, E. asburiae showed the capacity to produce IAA at all concentrations of tryptophan. Results of present study were in contrast to research data of Ahmad et al. (16) reported that auxin production increased in the presence of higher tryptophan concentrations, whereas, mechanisms of IAA biosynthesis including both tryptophan-dependent and independent pathways were reported (17-18). Although, the strains of E. asburiae isolated from nodule and rhizosphere, have been also reported for their abilities to produce IAA, there were not reports about their pathway for synthesis (19-20). Therefore, results of the present study, the production of IAA of E. asburiae may synthesized via tryptophan independent pathway. Further studies should be considered on their potential as bio-inoculants to increase the productivity of crops.