Bacterial rots are among the most serious diseases of onion that is being appeared in storage and/or transit. This research aimed to investigate effect of the combined application of Streptomyces coelicolor, and arbuscular mycorrhizal fungi (AMF) on controlling onion bacterial rots. S. coelicolor and AMF, individual or in combination, a significant decrease in the disease incidence was shown with superiority of the combined treatment. Total phenol content of plants and polyphenol oxidase and peroxidase enzymes were significantly increased in response to this application. However, a significant decrease in lipid peroxidation was recorded. According to their distinguished efficiency and known remarkable eco-safety, this combination can possibly be used in the biological control of bacterial rot diseases of onion. Further greater application may be tried.