Abstract: The optimization of ultrasound- assisted extraction process of total flavonoids from Caulis Lonicerae was investigated by response surface methodology( RSM) based on central composite design and the antioxidant activities in vitro of the extracted flavonoids was measured using 1,1- diphenyl-2- picrylhydrazyl( DPPH·) scavenging,2,2'- azino- bis( 3- ethylbenzthiazoline-6- sulfonic acid( ABTS+·) radical scavenging,Fe2 +chelating activity and ferric reducing antioxidant power( FRAP) methods.The results showed that the optimal ultrasound- assisted extraction conditions for total flavonoids from Caulis Lonicerae were obtained as follows: ethanol concentration was 70%,liquid- solid ratio 31 ∶ 1( m L / g),ultrasonic power 210 W,ultrasonic time8 min. Under these conditions,the yield of total flavonoids was 7.74% ± 0.10%. The extracted flavonoids exhibited powerful antioxidant activities in vitro. The IC50 of 1,1- diphenyl- 2- picrylhydrazyl( DPPH radical) scanvenging and ABTS+radical scanvenging capcities were 48.1,66.1 μg / m L,respectively. The EC50 of Fe2 +chelating ability was 83.6 μg / m L,and in the concentration range of 6.25~200 μg / m L,the linear regression equation of relationship between TRAP value and total flavonoids concentration from was as follow: Y = 0.0019 x + 0.1527( R2= 0.9964). This research might provide a theoretical basis for the further development and utilization of total flavonoids from Caulis Lonicerae.