The field experiments was carried out at the Horticulture Researches Sabhia Station , Horticulture Research Institute, Agriculture Research Center, Alexandria, Egypt during 2014 to 2016 in order to study the effect of potassium and biofertilization on growth, chemical composition of essential oil and major compounds of  rosemary (Rosmarinus officinalis L.). The experimental design was randomize complete block design with three replicates. The main results could be summarized as follows: (1) the K+ fertilization treatments, differently, affected the mean values of all studied characters, whereas the application treatment of (150 kg K2SO4/fed + NP mineral significantly, increased plant fresh and dry weights (g/plant), (2) the application of 300 kg K2SO4/fed + phosphorein + Ceraline treatment; gave the highest chemical composition (P and K%) and carbohydrate (%) during both seasons, whereas, the highest mean value of N% was recorded by 450 kg K2SO4/fed + Cerealin + phosphorein, and (3) the application of 20 L/fed Potassmage +  phosphorein + Ceraline; gave rise to the highest essential oil (%). Also, the various fertilizers; brought about the highest major's compounds (α- Pinene, β- Pinene, Cineol, Camphor, Borneol, Borneol acetate and Eugenol) percentages during  2015  season.