Objective:To observe the stabilizing action of Quyu Xiaoban Capsule on vulnerable plaque by using intravascular ultrasound（IVUS）.Methods:Twenty-three rabbits with balloon-induced abdominal aortic wall injury were fed with high fat diet.At the end of 12th week

20 of them were divided randomly into a natural regression group and a Chinese medicine group

10 for each group.At the end of 24th week

recombinant adenovirus carrying human wild type p53 gene were injected via a catheter into the aortic segments rich in plaques.Two weeks later

the plaque rupture was triggered by Chinese Russell’s Viper Venom and histamine.At the end of the 12th and 26th week

blood samples were taken to determine serum lipids and the abdominal aortas were detected with IVUS.The results were compared with pathological and electron microscopic results.Results:Compared with the natural regression group

total cholesterol（TC） and low density lipoprotein-cholesterol（LDL-C） in Chinese medicine group were significantly lower（P<0.05 and 0.01

respectively）.Extra-vascular elastic membrane area（EEMA）

plague area （PA） and lumen area stenosis percent （LAS%） in Chinese medicine group were significantly lower than those before treatment（P<0.05 or P<0.01）

with significant differences in morphological examination.Conclusion:Quyu Xiaoban Capsule can promote stabilization of vulnerable plaques.IVUS technique provides a reliable method for assessing the vlnerability of AS plaque.