Apelin is a bioactive peptide discovered recently that has been proved to be an endogenous ligand of the APJ receptor. Apelin and APJ are widely distributed in the central nervous system and peripheral tissues. Researches have confirmed that apelin/APJ involved in a wide range of physiological and pathological functions in the cardiovascular system. Investigations indicated that apelin is a novel critical factor in the development of atherosclerosis (AS). In this review, we discuss the roles of apelin in the vascular smooth muscle cell proliferation, monocytes-endothelial cell adhesion, and angiogenesis that potentially reveals a new cellular mechanism of AS. Considering these roles, apelin and APJ may be novel therapeutic targets of AS.