This study was carried out at the Experimental Farm of Medicinal and Aromatic Plants Research Department in El Kanater El Khairia, HRI, ARC, during the two successive seasons of 2016 and 2017 to study the effect of some microorganisms (Bacillus subtilis, Trichoderma harzianum, Pseudomonas fluoroscens andStreptomyces griseus) on suppressing of  damping-off disease of basil seedling, vegetative growth, oil production and chemical constituents of sweet basil (Ocimum basilicum L.) plants. The plants treated with any of the bioagents, showed highest effect in controlling damping-off and increased basil productivity compared with control plans. The results showed that, all bioagents treatments significantly increased vegetative growth (plant height, number of branches, fresh and dry weights (g/plant), oil percentage, oil yield, chemical constituents (chlorophyll (a), (b) and carotenoids contents as well as total carbohydrates percentage) compared with control plants. Streptomyces griseus gave the best effect against damping-off disease and all plant characteristics compared with control plants in the  first season while, in the second season, Pseudomonas fluorescens increased plant protection and all plant characteristics. GC analysis of sweet basil essential oil of all treatments identified nine components. The major component of the essential oils was Linalool.