Apolipoprotein A5 is a newly identified apolipoprotein. Although it is at low level in serum, it decreases plasma triglyceride level significantly. The gene polymorphism of apolipoprotein A5 is closely associated with plasma triglyceride level and atherosclerosis disease. We reviewed its structure, function and gene polymorphism, as well as its association with triglyceride and atherosclerosis disease.