Cardiovascular disease (CVD) has emerged as the leading cause of death worldwide. Acute coronary syndrome (ACS), one of the most harmful cardiovascular events, is, in most cases, triggered by the rupture of a vulnerable plaque followed by thrombosis formation at the rupture site. Deep understanding of vulnerable plaque formation can greatly impact therapeutic approaches for both prevention and treatment of acute cardiovascular events. In the article, we reviewed the concept, characteristics and the pathological mechanisms of vulnerable plaque.