Apurinic/apyrimidinic endonuclease 1/redox factor-1 (APE1/Ref-1) is a secretable multifunctional protein. Since the concept of APE1/Ref-1 secretion was established in 2013, several studies have demonstrated the usefulness of APE1/Ref-1 as a serological biomarker. However, the role of APE1/Ref-1 in atherosclerotic vascular inflammation is unclear. Herein, we investigated the role of APE1/Ref-1 in atherosclerotic apolipoprotein E (ApoE^-/-) mice fed with a Western-type diet as an animal model of vascular inflammation. We found that serologic APE1/Ref-1 was strongly correlated with vascular inflammation in these mice. Neutrophil/lymphocyte ratio, endothelial cell/macrophage activation, and atherosclerotic plaque formation, reflected by atherosclerotic inflammation, were increased in the ApoE^-/- mice fed with a Western-type diet. Correlation analysis showed a high correlation between plasma APE1/Ref-1 levels and neutrophil/lymphocyte ratio, a marker of systemic inflammation. We conclude that APE1/Ref-1 expression is upregulated in aortic endothelial cells/macrophages of atherosclerotic mice, and that plasma APE1/Ref-1 levels could predict atherosclerotic inflammation, it is a useful biomarker for vascular inflammation in atherosclerosis.