The influence of electro-acupuncture Neiguan point at different time on circadian rhythms of systolic time intervals of normal young male adults were studied in this work. It was found that the indices of STI of normal young male adults were all shown approximate circadian rhythms. The acrophase and significant level of rhythms could be changed by electro-acupuncture at Neiguan point, but the period of rhythms kept constant. The results show that the time factor plays an important role in the effects of acupuncture or electro-acupuncture. So acupuncture may be looked on as a chronizer and applied to modulate some rhythms.