1. Objectives The purpose of this research is to find out the Sasang Constitutional difference in Heart Rate Variability. 2. Methods We enrolled 8498 workers who tested for Heart Rate Variability(HRV) from September 1, 2005 to November 28, 2005 except works whose body constitusions were undetermined according to QSCCII. 3. Results & Conclusions The result of HRV of autonomic activity and stress resistance were arranged in the order of Soeumin, Soyangin and Taeumin. On the other hand Stress Index and Fatigue Index were arranged in the order of Taeumin, Soyangin and Soeumin. But autonomic balance was no significance relationship between Sasang Constitutions. This research has shown that there is a statistical significance between the HRV and Sasang Constitutions. The findings indicated that HRV could be useful mean to make a diagnosis of Sasang Constitution or apprehended Constitutional differences.