In this research, the effect of different extraction methods (hydrodistillation, ohmic assisted hydrodistillation, and ultrasound application as pretreatment) was investigated for chemical composition and physical properties of the essential oils obtained from Rosmarinus officinalis , and the effect on biological properties (antioxidant and antibacterial) was examined. The most time consuming method of extraction was hydrodistillation (162.67 min) and the least one was ohmic assisted hydrodistillation with the ultrasound pretreatment (67 min), due to simultaneous heating of the whole sample with a higher rate. There was no significant difference in the essential oil extraction yield and its physical properties. The main components of the studied essential oils are ?-pinene (14.23-16.25%), camphor (8.73-9.87%), bornyl acetate (8.34-9.97%) and 1,8-cineol (7.11-8.46%). Evaluating the antioxidant activity of the obtained essential oils and comparing to the commercial antioxidants, BHT and BHA, showed no valuable antioxidant property of the essential oil. The micrographs revealed the impact of the extraction methods on the destruction of the essential oil glands. Key Words: Essential oil, Extraction, Ohmic extraction, Rosemary, Ultrasound
