Aim S-adenosylhomocysteine (SAH) is involved in the epigenetic mechanism of hyperhomocysteinemia pathogenicity of atherosclerosis, but the underlying mechanisms remain unclear.Here, we tested the hypothesis whether SAH affects atherosclerosis via epigenetic regulation of endoplasmic reticulum stress pathways.Methods and Results Apolipoprotein E-deficient (ApoE-/-) mice at eight weeks of age were fed one of four diets for 16 weeks: control, high-methionine (10 g/kg food), adenosine periodate oxidized (40mg/kg food) (ADA, the inhibitor of SAH hydrolase to prevent cleavage of SAH to homocysteine and adenosine), or ADA combined methionine.ADA supplement significantly reduced the protein expression and activity of SAH hydrolase, and then elevated plasma SAH levels.Atherosclerotic lesion size was significantly increased in ADA or ADA combined methionine diet-fed mice compared with control mice.Correlation analyses showed that plasma SAH was linked with atherosclerotic lesion independent of plasma homocysteine.Expressions of endoplasmic reticulum stress markers (GRP78, CHOP) were significantly increased in the mice with elevated plasma SAH levels.Moreover, plasma SAH was associated with the inhibition of trimethylation of histone H3 lysine 9 (3meH3K9)Chromatin immunoprecipitation assay showed a decrease in levels of suppressor chromatin marker 3meH3K9 in the promoter regions of GRP78 and CHOP in the plasma SAH accumulated mice.Conclusion SAH accumulation promotes the development of atherosclerosis independent of plasma homocysteine by epigenetic regulation of endoplasmic reticulum stress pathways.