The objective of this prospective cohort study is to evaluate the Heart rate variability as a predictor of mortality in septic patients. Each patient underwent a 20-minute Holter and a 24-hour Holter on the first day of enrollment. In 20-minute Holter, several HRV parameters of nonsurvivors were significantly lower than those of survivors. SDNN ≤17 is a risk factor for death in septic patients, even after adjusting for severity scores. Predictive power of the SDNN + SOFA model is better than predictive power of SOFA only.