Aim To assess the character of carotid atherosclerosis in patients with cerebral infarction and the relationship with serum matrix metalloproteinase-9 (MMP-9). Methods The duplex ultrasonography was performed in the carotid arteries of all the 120 patients with cerebral infarction located in arteriae carotis interna system. 84 patients were included and were divided into soft plaque group, hard plaque group and nonplaque group. Serum MMP-9 levels were determined by enzyme-linked immunosorbent assay in blood samples obtained 3 weeks later after hospitalization. Results Carotid plaques were found in 87 (72.5%)patients, the prevalence of severe lumen stenosis was 4.17%. The incidence of soft plaque in the side of cerebral infarction were higher than that of non-infarction. Serum MMP-9 levels were significantly higher in soft plaque group than those in the hard plaque and non-plaque group (p<0.05). Conclusions Most of the carotid artery lesion are plaques other than severe stenosis, which may be the character of carotid atherosclerosis of Chinese stroke patients. Soft plaque is an important risk factor of stroke in our study. MMP-9 may be a potential clinical marker of unstable plaque.