Aim To observe Helicobacter pylori (Hp) infection situation in patients with different degree of carotid atherosclerotic stenosis, and to examine the level of serum lipoprotein-associated phospholipase A₂ (Lp-PLA₂) and matrix metalloproteinase-9 (MMP-9); To analyze the relationship between Hp infection and carotid atherosclerosis, and to explore possible mechanism of carotid atherosclerosis caused by infection. Methods From September 2012 to September 2013 in our hospital, a total of 128 patients with carotid atherosclerosis confirmed by carotid artery ultrasound was analyzed. The carotid artery stenosis patients were divided into three groups:severe stenosis group (stenosis rate≥70% to nearly occlusion; n＝48), moderate stenosis group (stenosis rate 50%～69%; n＝45), mild stenosis group (stenosis rate＜50%; n＝35). Normal carotid artery individuals were as a control group (n＝20). Serum Hp antibody (Hp-IgG), Lp-PLA₂, and MMP-9 levels were examined by enzyme-linked immunosorbent assay (ELISA). Results (1)Hp-IgG positive rate was significantly higher in patients with carotid atherosclerosis than that in the control group (64.1% vs 30.0%, P<0.05). Hp-IgG positive rate was 75.0% in severe stenosis group, 62.2% in moderate stenosis group, and 51.4% in mild stenosis group, which was significantly higher than that in control group (P<0.05). (2)The serum concentrations of Lp-PLA₂ and MMP-9 in Hp-IgG positive group were significantly higher than those in Hp-IgG negative group (P<0.05). (3)The serum concentrations of Lp-PLA₂ and MMP-9 in severe, moderate and mild stenosis groups were significantly higher than those in control group (P<0.05). Conclusions (1)Hp infection can increase the risk of carotid atherosclerosis. With the aggravation of Hp infection, carotid stenosis has a tendency to increase. (2)Hp infection may enhance the local inflammatory response to promote and aggravate carotid atherosclerotic stenosis through the increase of inflammatory cytokines Lp-PLA₂ and MMP-9.