In general, anesthetic depth is evaluated by experience of anesthesiologist based on the changes of blood pressure and pulse rate. So it is difficult to guarantee the accuracy in evaluation of anesthetic depth. The efforts to develop the objective index for evaluation of anesthetic depth were continued but there was ression in this area. In recent EEG, evoked potential and law esophageal pressure are testad as monitoring tools of anesthetic depth. Heaut rate variabilty provides much infarmation of autonomic activity of cardiovascular system and almost all anesthetics depress the autonamic activity. Novel monitoring system which can simply and exactly analyze the autonomic activity of cardiovascular system will provide important information for evaluation of anesthetic depth. In this aspect, development of real time R-R interval variability analysis system and evaluation of its efficacy for evaluation of anesthetic depth were performed. Newly developed real time R-R interval variability analysis system works by simple adaptation to EKG monitor, displays the color power spectrum every 30 seconds for at least 4 hours. So users can easily understand the whole trends during anesthesia and check the changes of short duration. And for the cutting expenditure of memory of personal computer this system is programmed to discard the calculated data of power spectrum after display on screen and saves only R-R interal of heart rate for off-line analysis. At first, function of real time R-R interval variability analysis system was tested with EKG simulator. Our system was well functioned in getting the signals from EKG, analyzing, displaying and saving the data. In animal experiment the changes in power of high frequency band assaciated with the changes of end tidal concentration of halothane (p<0.05). And during intravenous infusion of propofol the changes of infusion amount induced the changes in power spectrum of each frequency band. After animal experiment clinical application was tried. During induction of N2O-O2-enflurane anesthesia and recovery, power of each frequency band was decreased and increased in trend. Endotracheal intubation and skin incision induced high peak of power of each frequency band. Standard score of power and trend curve using 3RSSH was used for the analysis of trend of power change and provide meaningful information of R-R interval variability.