Obstructive sleep apnea syndrome (OSAS) is characterized by repetitive episodes of upper airway obstruction during sleep. The prevalence of OSAS in middle-aged population is about 2%-4%.1 Many OSAS patients can be accompanied by serious cardiovascular complications, such as hypertension.2 The aim of this study was to find the changes of autonomic nervous system (ANS) during sleep, and the impact of surgical treatment on heart rate variability (HRV) in OSAS patients.