To study the chemical compositions,antioxidant activity and antibacterial activity of essential oil of rosemary,the essential oil ofRosmarinus officinalis L.(rosemary) was extracted by steam distillation and the chemical compositions were analyzed by GC-MS.The antioxidant activity in vitro of essential oil was evaluated by DPPH free radical,hydroxyl free radical scavenging activity and reducing power.The antibacterial activity of rosemary essential oil was studied by measuring the size of the inhibition zone and the minimum inhibitory concentration (MIC) with Bacillus subtilis,Staphylococcus aureus and Escherichia coli as test bacteria.The results showed that 40 chemical components were identified from the essential oil of rosemary,accounting for 99.46% of the total essential oil.The main chemical components were α-pinene (39.05%) and 1,8-cineole (16.86%),followed by camphene (4.22%),D-limonene (3.87%),borneol (3.74%),β-caryophyllene (3.11%),etc.The content of α-pinene was higher than other regions in China.The half of the clearance IC₅₀ values of DPPH,hydroxyl free radical and reducing power of rosemary essential oil were 76.42,51.40 and 49.15μL/mL.The inhibitory zone sizes of essential oil against B. subtilis,S. aureus and E. coli were 14.40±0.66,11.41±0.19 and 11.70±0.27 mm.The minimum inhibitory concentration (MIC) of essential oil against  B. subtilis,S. aureus and E. coli were 2.50,10.00,10.00 μL/mL.The inhibition of B. subtilis was stronger than that of S. aureus and E. coli.The results suggested that rosemary essential oil had strong antioxidant and antimicrobial activities.