The autonomic nervous system, which consists of sympathetic and parasympathetic nerves, plays an important role in the regulation of various functions of body organs. Recent studies have reported that vagal afferents that transmit information from the periphery to the brain function as an important signal pathway for dissemination of details regarding nutritional status, as well as the cardiovascular system and inflammation. In this review, we describe the measurement analysis of vagal nerve activity in mice using an in vivo electrophysiological method and account for the role and mechanism of action of vagal nerves in homeostasis.