A carbon fiber electrode was developed to detect sympathetic nerve activity for purpose of physiological artificial heart control. Contact impedance of a carbon fiber electrode was between that of collagen fiber electrode and Ag electrode. Renal sympathetic nerve activity was recorded by means of the carbon fiber electrode in intact nerve of rabbits. Relationship of heart rate and integrated renal sympathetic nerve activity(IRSNA)was shown quantitatively by recording vital reaction at administration of ganglionic-blocking agent. In chronic experiment, renal sympathetic nerve activity was able to be recorded during two weeks in awake rabbits. These results indicate that there is an ability to detect sympathetic nervous system activity and application to artificial heart control in this carbon fiber electrode.