Attempts to induce genetic improvement in Azotobacter chroococcum wild type strain, identify their new mutants were conducted in this present work.  The study was extended to evaluate their efficiency to promote some growth and quality traits of sweet melon (Cucumis melo L.) cv. Kahera 6 seedlings. After treatment of Azotobacter chroococcum wild type with different concentrations (50, 100 and 200µg/ml) of the mutagen N-Methyl-N’-nitro-N-nitrosoguanidine (MNNG) for three times (30, 60 and 120 min), it was observed that the numbers and percentages of treated colonies were decreased by increasing the concentration and time of exposing to mutagen. The obtained number of Azotobacter chroococcum mutants was 15 auxotrophs which symbolized from FM1 to FM15. Among them, ten mutants were identified according to their specific auxotrophic requirements. It was found that 6 mutant cells had a single mutation: Isoleucineless (Isoleu^-), Aspartic acid less (Asp^-), Histidineless (His^-), Prolineless (Pro^-), Glutamic acid less (Glu^-) while the other mutant cells were carried a double mutation: Vit.B1^-/Thr^-, Thr^-/Thi^-, Orn^-/ Asp^- and Vit.B9^-/Vit.B6^- . All strains were tested for their antibiotic resistance, pH and salinity tolerance properties. The obtained results revealed that there was possible genetic variation among them. Concerning the effect of wild type and their mutant strains in growth and quality of sweet melon seedling, it was found that almost of mutants were superior to wild type and untreated control treatments in germination percentages and growth traits particularly the four mutant strains FM12, FM13, FM8 and FM9. Inoculation of sweet melon plants with almost of tested Azotobacter chroococcum strains particularly the three mutants (FM12, FM13 and FM8) increased the uptake of leaves N, P and K and photosynthetic pigments contents as compared to wild type and untreated control treatments. Finally, it could be concluded that treatment of Azotobacter chroococcum wild type strain with different MNNG concentrations may produce a new genetic parameter (Genotype) which could be used as a desirable bio-inoculates to improve growth and quality of sweet melon seedlings.