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 1600m³/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 m³/fed. On the other hand, the highest oil percentages and oil yield/ plant resulted under the effect of irrigation at 800 m³/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 m³/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 m³/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 m³ 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 naturally-occurring 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