Organometallic compounds and complexes possibly show novel bioactivities unprecedented with organic molecules that consist of C, H, O, and N atoms. We have already reported that an organoantimony compound selectively induces the expression of perlecan, a large heparin sulfate proteoglycan, in cultured vascular endothelial cells. Perlecan consists of a core protein with Mr of approximately 400 kDa and three anticoagulant heparan sulfate glycosaminoglycan chains. However, little is known about the molecular mechanisms of perlecan expression in endothelial cells. Since an organoantimony compound induces the expression of perlecan, we prepared a variety of its derivatives and tried to identify the binding proteins for the organoantimony compound by the drug affinity responsive target stability method, a negative selection method to identify the target proteins. As the results, we found glucocoriticoid receptor as binding protein of the organoantimony compound, which mediates the expression of perlecan in endothelial cells.