This study was carried out during the two successive growing seasons of 2018/2019 and 2019/2020 at the Farm of Ali Mubarak, South Tahrir, El-Bahira Governorate, Horticulture Research Station. Egypt, aiming to study the impact of some bio-fertilizers (Mycorrhiza, Algae, and PGPR) combined with 3 levels of irrigation (800, 1200, and 1600m 3 /fed treatments and their interactions on vegetative growth, essential oil %, essential oil components, N, P, K%, and proline content of rosemary (Rosmarinus officinalis L.) plant grown in a sandy soil. The obtained results could be summarized as follows; a significant increase in plant height, number of branches, and fresh and dry weights per plant were recorded with irrigation at 1200 m 3 /fed. On the other hand, the highest oil percentages and oil yield/ plant resulted under the effect of irrigation at 800 m 3 /fed biofertilizer treatments also, increased vegetative growth parameters i.e., plant height, number of branches, herb fresh and dry weights/ plant and oil percentage, and yield/plant. Irrigation at the rate of 1200 m 3 /fed, and PGPR alone or their combination resulted in the highest values of the above-mentioned traits (plant growth, parameters). However, the combination between irrigation at 800 m 3 /fed and PGPR showed the highest values of oil percentage and oil yield/plant. The N, P and K% in dried herb recorded their higher values with medium irrigation, i.e., at the rate 1200 m 3 in both cuts. Also, the results showed that there was a steady significant increase in proline content due to decreasing the irrigation rate. This investigation supports the application of naturallyoccurring plant growth promoting rhizobacteria (PGPR) and microorganism to advance plant development and sustainable option for farmers under deficit water to maximize the yield of rosemary plant.