Diabetes mellitus (DM) is a kind of chronic metabolic disease characterized by chronic hyperglycemia and glucose intolerance. Recently, with the increasing incidence of DM, it has become one of the major threats seriously affecting human health. DM will lead to chronic damage and dysfunction of vasculatures within various tissues and organs, causing serious complications. Modern optical imaging techniques offer essential tools for accurate evaluation of the structural and functional changes for DM-targeted organs/tissues, which provide valuable information for the early diagnosis and therapy of diabetes. This chapter will introduce the structural and functional changes of vasculatures induced by DM within the kidneys, skin, and cerebrum, as well as how novel optical imaging techniques for in vitro and in vivo can be used to study these changes induced by diabetes.