Background: Recently with the advent of the chaos theory and computer technology, physicians could analyze the heart rate variability(HRV) which reflects autonomic control of cardiac disorders and autonomic diseases. In compensatory phase of hemorrhagic shock, autonomic nervous system plays major role in maintaining near-normal hemodynamic to preserve tissue perfusion, In this thesis, the clinical feasibility of HRV as a new tool for the assessment of seventy and responsiveness to treatment during early phase of hemorrhagic shock was studied. Methods. The PSA of HRV was performed using fast Fourier transformation algorithm with 512 RR interval data recorded off - line by Holter system. Each components of PSA were compared between patient and control group, each consisted of 19 patients. Results: On presentation to emergency department, the patient group showed significantly lower very low frequency (VLF) band, low frequency (LF) band, high frequency(HF) band, low frequency normalized unit (HFnu) and high frequency normalized unit (HFnu) than control group. After stabilized, LF and Lfnu decreased in the patient group compared to initial phase but there was no statistical significance As fluid resuscitation started and continued, LF/HF ratio increased and then stabilized thereafter, In one full recovered patient, LF/HF ratio obtained dung one hour penod on the 20 th hospital day showed very unstable and dynamic change which may represent homeodynamic rather homeostasis. Conclusion: The PSA of HRV seemed to be potential tools in the diagnosis and monitoring of hemorrhagic shock. Well-designed further studies are expected for the refinement in data processing and interpretation of results of PSA of HRV.