Proteoglycans are macromolecules comprising a core protein and one or more glycosaminoglycan side chains. The macromolecules particularly derived from vascular smooth muscle cells accumulate in atherosclerotic vascular wall and are involved in the progression of vascular lesions. However, the functions of proteoglycans depend on the type of core proteins and microstructure of glycosaminoglycan chains, suggesting importance of the regulation of proteoglycan synthesis in vascular smooth muscle cells. Although the regulation of glycosaminoglycan chain formation is not clear, core protein synthesis is regulated by growth factors/cytokines, mechanical strain, coagulation factors, and other factors. Recently, we found that adiponectin, an adipose-specific plasma protein that exhibits antiatherogenic activities, regulates proteoglycan synthesis in vascular smooth muscle cells.