Abstract: AIM To observe the dynamic changes of cardiac autonomic nervous function in rabbits under different depth of urethane anesthesia. METHODS An analysis of heart rate variability (HRV) was used to quantify the influence on the drive of cardiac autonomic nerves and the balance control of heart rate in rabbits with urethane anesthesia of different accumulated doses (0.50, 1.00, 1.25, 1.50, 1.75, 2.00, 2.25 and 2.50 g/kg). RESULTS The time domain components: Compared with heart rate (HR) at dose 0.50 g/kg, the HR increased at doses 1.25, 1.50 and 1.75 g/kg (P<0.05 ) and there was a corresponding decrease in RR interval (RRI). The value of the standard deviation of all normal RR intervals (SD) decreased at doses higher than 1.00 g/kg（P<0.05 or P<0.01） and the total power variability of HR (TV) decreased at doses higher than 1.25 g/kg（P<0.05 or P<0.01. The frequency domain components: Compared with the value of low frequency power (LF) at dose 0.50 g/kg, the value of LF decreased at doses 1.25, 1.50, 2.00, 2.25 and 2.50 g/kg（P<0.05, respectively）but there were no significant changes in the value of the normalized low frequency power (LFn) at other doses. The value of high frequency power (HF) showed no significant changes at all the accumulated doses but the normalized high frequency power (HFn) increased markedly (P<0.05 ) at doses higher than 1.25 g/kg. The ratio of low to high frequency power (LF/HF) decreased significantly (P<0.01) at accumulated doses higher than 1.00 g/kg. CONCLUSION HRV decreases in rabbits under different accumulated urethane anesthesia may come from the significant increase in cardiac vagal nerve activity.