Adiponectin, which is an adipose-specific plasma protein, exhibits antiatherogenic activities. The purpose of the present study is to demonstrate that adiponectin regulates the synthesis of proteoglycans—macromolecules comprising a core protein and glycosaminoglycan side chains involved in atherosclerosis progression—in vascular smooth muscle cells.In the present study, proteoglycans obtained from cultured, adiponectin-treated human coronary artery smooth muscle cells were characterized using biochemical techniques.The results indicated that adiponectin induces the synthesis of decorin—a small dermatan sulfate proteoglycan—in vascular smooth muscle cells. Furthermore, the length of dermatan sulfate chains of the decorin molecule appeared to remain unchanged, but the epimerization of glucuronic acid in the chains decreased.Although the significance of the regulation of decorin synthesis in atherosclerosis progression by adiponectin remains to be determined, the present study demonstrates for the first time that adiponectin regulates proteoglycan synthesis in vascular smooth muscle cells.