Essential oil of Rosemary (Rosmarinus officinalis L) was solvent-free microwave extracted and analysed by GC/MS. 36 compounds were identified, and the main constituents of the oil included 1,8-cineole (16.87%), camphor (24.12%), alpha-pinene (11.04%), beta-pinene (5,51%) etc, ... The results demonstrate that rosemary essential oil exhibited free radical scavenging activity against DPPH with IC50 = 472.46 mu g/ml. Rosemary oil has also been proven effective against all of examined pathogens except P. aeruginosa. The Minimum Inhibitory Concentration (MIC) was 8 mu l/ml for Salmonella typhimurium and 4 mu l/ml for the other four studied strains (Enterococcus faecalis, Staphylococcus aureus, MRSA, Escherichia coli). These results will open new venues for rosemary oil medical use.