Mechanisms responsible for atherosclerotic plaque development, destabilization, and rupture are still largely unknown. Angiotensin II, the main bioactive peptide of renin angiotensin system, has been shown to be critically involved in the pathogenesis of atherosclerosis and vulnerable plaque. Experimental studies in hypercholesterolemic mouse models with high circulating Angiotensin II levels, provide direct evidence that Angiotensin II induces plaque vulnerability partly by 1/ downregulating vascular expression of anti-atherosclerotic genes and/or upregulating expression of pro-atherosclerotic genes, and 2/ skewing the systemic lymphocyte Th1/Th2 balance towards a proinflammatory Th1 response in early disease phase. Further understanding the pro-atherosclerotic mechanisms of Angiotensin II and associated signaling pathways will help to design better therapeutic strategies for reducing the burden of atherosclerotic cardiovascular disease.