Objectives : Assuming that the characteristic of meridian system has been similar to this of electric potentials in human body and that measurements of electric potential at well(井穴) and sea(合穴) points in branches of the twelves meridians will be representative of measurements of the twelve meridians, to measure the electric potentials in twenty aged(TAG) and fifty aged(FAG) healthy volunteers groups when they were sleeping or awakening respectively, to do significance test for electric potential of meridian system among circadian rhythms(CR) and Sasang constitutions(SC). Methods : We selected who thirty healthy volunteers were diagnosed by a blood test, urine examination and differentiation of syndromes by five viscera among volunteers. When they were sleeping, their electric potentials of well and sea points in branches of the twelve meridians were simultaneously measured by physiograph. After a minute we measured them again, totally 5 times. And then when they were awakening, their electric potentials were measured 5 times by the above method. Results : Measurements were analyzed by statistical ANOVA test, we obtained that some of the electric potentials of TAG at sleeping significantly varied with CR, SC, and at awakening some of the electric potentials of FAG also significantly did with CR, SC.