This study was carried out in the Nursery of Floriculture, Ornamental Horticulture and Landscape Gardening Department, Faculty of Agriculture, Alexandria University, during the two successive seasons of 2017 and 2018. The aim of the present investigation was to evaluate the effect of seaweed extract and active dry yeast on vegetative growth and oil yield of Ocimum basilicum L. The layout of the experiment of both seasons was split-plot design in three replicates. Each replicate contained 20 different treatments (4 levels of dry yeast x 5 levels of seaweed) five plants were used as a plot for each treatment. The main plot represented the active dry yeast at the concentrations of 0,2,4 and 6 g/l which sprayed on plant leaves. The sub-plot was seaweed extract at the concentrations of 0, 1, 2, 3 and 4 g/l added as a foliar application. The most of vegetative growth and yield traits responded significantly to the combination of active dry yeast with seaweed extract as biofertilizer on basil plants. Plant height, number of leaves, leaves dry weights and leaf area were significantly affected with spraying plants by dry yeast and seaweed. As a general, the treatment namely 6 g/l + 4 g/l gave the best combination between the dry yeast and seaweed.  The best oil percentage was recorded by using 4 g/l dry yeast with 4 g/l seaweed in the first cuts of both seasons and by using 6 g/l dry yeast with 4 g/l seaweed in the second cuts in both seasons. The major components of sweet basil essential oil were linalool, giving the highest percentage (52.16-79.55%) by using 6 g/l dry yeast with control (0 g/l) seaweed. Estragole, recorded the highest percentage (5.14-11.79%) by using 6 g/l dry yeast with 1 g/l seaweed. Eucalyptol, gave the highest percentage (1.54-9.72%) by using 4 g/l dry yeast with 2 g/l seaweed. Methyl cinnamate, the highest percentage (1.12-10.37%) was produced by using 0 g/l dry yeast with 4 g/l seaweed. Tau-cadinol, the highest percentage (1.01-6.97%) was obtained by using 2 g/l dry yeast with 2 g/l seaweed. Trans-α-bergamotene, the highest percentage (1.23-5.18%) was resulted by using 0 g/l dry yeast with 0 g/l seaweed. Bornyl acetate, gave the highest percentage (1.12-4.53%) was obtained by using 2 g/l dry yeast with 4 g/l seaweed. Form this study we recommend economically and environmentally to fertilize sweet basil by spray bio fertilization as dry yeast at the rate 4 or 6 g/l with spray the plants by seaweed at the rate 4 g/l to obtain the best growth, oil yield, and safe for human being chemical composition of Ocimum basilicum L.