Objective To observe the effects of different herbal extractives on vulnerable atherosclerotic plaque stability in the aortic roots of fat-fed ApoE knockout mice.Methods Sixty ApoE knockout mice were fed a high-fat diet for 13 weeks until the mature atherosclerotic plaques formed.Thereafter

they were randomized into five groups:activating blood circulation group （treated with tanshinone）

reinforcing qi group （treated with panaxquinquefoliumsaponin）

dissolving phlegm group （treated with snakegourd fruit extract）

control group

positive control group （treated with simvastatin）.The treatment lasted for 13 weeks.The morphological method and vulnerability index were used to evaluate comprehensively the effect on the vulnerable atherosclerotic plaque stability.Results Compared with the control group

the vulnerability indexes of 3 herb groups were decreased.There was significant difference in the ratio of the length of fibrous cap to plaque intima

and the number of buried caps in plaque of dissolving phlegm group （snakegourd fruit extract） was significantly decreased.Conclusion The herbal extractives with the effect of activating blood circulation

reinforcing Qi and dissolving phlegm can stabilize vulnerable plaque by changing plaque composition.The snakegourd fruit extract is more superior on reducing the frequency of plaque rupture

its concrete mechanism is worth further investigating.