Ultrasound assisted extraction (UAE) of saikosaponins from Radix Bupleuri (Bupleurum Chinense DC) was studied. The effects of various factors such as time (t), temperature (7), ultrasound power (1), particle size (S), solvent to solid ratio (R) and solvent concentration (C) on the yield of target components were investigated. The experimental results indicated that the extraction by UAE is six times faster than those by conventional thermal extraction. It is also found that fast extraction rate was obtained in the first 30 min of sonication. Prolonged sonication did not give a proportional increase in the yield. For the effect of ultrasound power, the maximum yield was obtained at the power level of around 21 W. Scanning electron microscope (SEM) images of the plant cells after UAE treatment were obtained to provide visual evidence of the somication effect. The effects of particle size, solvent to solid ratio and solvent concentration on the yield are also discussed. The preliminary optimum conditions for UAE of saikosaponins were found at time of 30 min, temperature of 80 degrees C, power of 21 W, particle size < 0.3 mm, solvent to solid ratio of 25 ml/g and solvent concentration of 50%. (c) 2007 Elsevier B.V. All rights reserved.