Two field experiments were conducted in a calcareous soil at El-Noubaria Research Station (ARC) during two successive seasons (2006 and 2007) to study the effect of biofertilizer inoculation with nitrogen fixing bacteria (Azospirillum lipoferum, Azotobacter chrococcoum, Bacillus polymyxa and Klebsiellapneumoniae), K-solubilizing bacteria (Bacillus circulans) and Arbuscular mycorrhizal fungi on growth, yield and different storage periods of onion (Allium cepa) cultivar Giza 20. The important obtained results are as follows: Plant height and number of tubular leaves, plant dry weight and yield as growth parameters, nitrogenase enzyme activity, dehydrogenase enzyme activity and the percentage of AM-mycorrhizal infection as microbiological parameters and total nitrogen, phosphorus, potassium and carbohydrates as chemical parameters gave more vigor growth and yield due to the inoculation with N2-fixers + Bacillus circulans + AM-mycorrhizae + ½ dose of NPK fertilizers compared to control during both tested seasons and that also they recorded best plant growth, harvest bulbs yield (12.7 and 13.7 ton/fed), onion chemical properties as well as increased the tolerance against diseases and maintained healthy bulbs during the different storage periods.