Disclosed is use of selenoprotein P in the diagnosis or treatment of type-2 diabetes or a vascular disorder. Specifically disclosed are: a method for detection of type-2 diabetes or a vascular disorder, comprising measuring selenoprotein P; a method for evaluation of the risk of being suffering from type-2 diabetes or a vascular disorder; a method for evaluation of the insulin resistance or blood glucose control in a subject; and a therapeutic agent for type-2 diabetes or a vascular disorder which is targeted to selenoprotein P.