A greenhouse nursery study was conducted to assess the interactive effects of arbuscular mycorrhizal (AM) fungus (Glomus mosseae) and nitrogen-fixing bacteria (Azotobacter chroococcum) on leading microorganisms group, growth, and nutrition of onion plants grown in unsterile calcareous soil in a greenhouse pot experiment. The results showed that Glomus mosseae and Azotobacter chroococcum significantly (P=0.05) increased bacterial, actinomycetes, Azotobacter count, and nitrogenase activity in onion rhizosphere. Moreover, coupling both organisms significantly increased sporulation and mycorrhizal infection of onion plant roots. Dry weight, nitrogen, and phosphorus uptake of shoots of dually inoculated plants were far higher than of shoots of plants inoculated with either microorganisms. It could conclude that microbial soil co-inoculation Glomus mosseae and Azotobacter chroococcum significantly enhance plant growth, N and P uptake of onion, and the strategy may be applied to obtain better crop productivity.