Rosmarinus officinalis is one of the most important medicinal and aromatic plants around the world. Essential oil as a weapon against biotic and abiotic stresses plays an important role in essential oil bearing plants. In this study the essential oil content and constituent of plants containing bacterium-gall on the shoots and crown was compared with non-contaminated plants. Essential oil percentage was extracted by hydro-distillation using Clevenger trap. Identification of the essential oil compounds was done by GC/MS. Results in essential oil percentage showed that, contaminated plants were relatively lower than that of non-contaminated plants per 100 grams of dry leaves. GC/MS also, verified that α- pinene and Camphor, respectively were 1.43% and 7.02%, more in contaminated plant than non-contaminated plant. In addition, Berbenone (18%), was the most common constituent which had been observed only in contaminated rosemaries. The analysis of leaf extract using HPLC, showed that the content of rosmarinic acid of healthy plants was significantly lower than that of contaminated plants. In addition, contaminated plants had total phenol and flavonoid compounds as well as antioxidant activity in the highest amount. Based on the obtained results, it can be concluded that, gall bacteria had influence on the phenolic components which are known as secondary metabolites in this medicinal plant and phenolic derivatives may be modified in quantity and quality by the affection of this biotic stressor, this could be considered as an application for further usage in metabolic culture.