Objective：To investigate the role of genetic polymorphisms of ApoE in carotid atherosclerosis（CAS） and the instability of the plaque. Methods：Totally 238 subjects were divided into 3 groups：instable plaque group，stable plaque group and control group according to the results of carotid ultrasound examination. The genotype of ApoE and serum ApoE concentration was measured. The relationship between the genetic polymorphism of ApoE and the instability of carotid plaque was studied using linear and logistic regression analysis. Results：①The frequency of ε4 allele in the CAS subjects was higher than that of health people（ χ2=5.78，P=0.020）. ②The average internal-media thickness（IMT） of subjects with ε4 allele was 1.22 mm，which was significant thicker than that of subjects without ε4 allele. ③The ApoE ε4 allele was an independent relative for the instable plaque when age，sex and blood fat were adjusted in logistic regression analysis. ④The levels of hypersensitive c-reactive protein（t=4.868，P=0.000） and monocyte chemoattractant protein-1（t=7.223，P=0.000） in serum of subjects with allele ε4 were higher than those in subjects without ε4 allele. Conclusion：ApoE polymorphism is associated with CAS and the instability of plaques. Patients with ApoE4 have severer CAS than subjects without ApoE e4 allele. The genetic polymorphism of ApoE has influenced the arteriosclerosis through adjusting the blood-fat or the chronic inflammation status.