OBJECTIVE: To explore the nocturnal variation of autonomic nervous system (ANS) in patients with obstructive sleep apnea syndrome (OSAS) and the transformation after surgery. METHOD: Sixty-one subjects with OSAS were recruited to undergo 7-hour nocturnal polysomnography(PSG) in sleep lab. Sixteen subjects with OSAS were performed PSG before and after UPPP. Sixteen subjects without OSAS were included as controls. Power spectrum analysis of heart rate variability (HRV) was performed in each subject. RESULT: The nocturnal of ANS activities were abnormal in patients with OSAS, especially the enhancement of sympathetic nervous activity. It increased gradually along with aggravating condition. The activities of sympathetic and vagus nerve were decreased significantly. CONCLUSION: There are abnormal ANS activities in patients with OSAS. Effective treatment of OSAS by surgery will significantly reduce the parameters of ANS, and redress the abnormality of heart rate and blood pressure.