OBJECTIVE: To investigate the cardiac autonomic nerve function in girls with idiopathic central precocious puberty (ICPP). METHODS: A total of 66 girls with ICPP were enrolled, among whom 36 were obese and 30 were not obese. A total of 68 age-matched healthy girls (normal controls) and 51 girls with simple obesity were enrolled as controls. All the subjects underwent 24-hour ambulatory electrocardiography, and deceleration capacity of heart rate (DC), acceleration capacity of heart rate (AC), and heart rate variability (HRV), and body mass index (BMI) were compared between groups. RESULTS: Compared with the normal control group, the ICPP group had significantly lower DC, standard deviation of normal-to-normal R-R intervals (SDNN), standard deviation of the average normal-to-normal intervals (SDANN), root mean square of successive differences (RMSSD), and high-frequency power (HF) and significantly higher AC and BMI. The ICPP group had significantly lower RMSSD and BMI than the simple obesity group (P<0.05). Compared with the ICPP girls without obesity, those with obesity had significantly lower DC, RMSSD, and HF and significantly higher AC and BMI (P<0.05). CONCLUSIONS: Cardiac autonomic dysfunction is seen in girls with ICPP, especially those with obesity, mainly presenting with reduced vagal tone.