Objective To investigate the effect of lactobacillus acidophilus on the expression of nitric oxide (NO) and its oxidative mediators, and to explore the anti-atherosclerosis mechanism of lactobacillus acidophilus. Methods Twentyfour male SPF rats were randomly divided into normal diet group, high-fat diet group and lactobacillus acidophilus group, with 8 rats in each group. The rats in the normal diet group were fed with normal diet, and the high-fat diet group was fed with high-fat diet + intraperitoneal injection of vitamin D3 + immune injury + FeSO4 to establish an atherosclerosis model. The rats in the lactobacillus acidophilus group were intragastrically administered with 0.5 mL of lactobacillus acidophilus per day (1×109 CFU/mL) on the basis of the high-fat diet. Rats were weighed at the 4th, 8th and 12th weekends. After 12 weeks of feeding, the serum was taken from abdominal aorta to detect the contents of oxidized low density lipoprotein (oxLDL), NO, arginine, arginase, and peroxynitrite (ONOO-). The aorta was isolated to observe the morphological change by HE staining. The expressions of eNOS and iNOS mRNA were detected by Real-time PCR, and the expressions of NF-κB p65 subunits were detected by Western blot assay. Results (1) There was no significant difference in body weight between the high-fat diet group and the lactobacillus acidophilus group during the whole experiment (P＞0.05), but both were significantly increased compared with those of the normal diet group (P < 0.01). (2) HE staining showed that the aorta formed a wide range of atherosclerotic lesions in the high-fat diet rats, and the aortic morphology was significantly improved in the lactobacillus acidophilus group. Only endothelial cell proliferation was found, and no smooth muscle cell necrosis was observed in this group. (3) Compared with normal diet group, the serum expressions of oxLDL, ONOO- , arginase, aortic iNOS mRNA and nuclear NF-κB p65 were increased in high-fat diet group (P＜0.01), and the serum arginine content and aortic eNOS mRNA expression levels were decreased (P＜0.01). While lactobacillus acidophilus can just reverse the above changes (P＜0.01). Conclusion Lactobacillus acidophilus may exert anti-atherosclerotic effects by regulating the expression of NOS, increasing NO bioavailability, and protecting endothelial function. [ABSTRACT FROM AUTHOR]