Objective:To investigate the changes of the autonomic nervous system (ANS) activity induced by obstructive sleep apnea (OA) during different sleep stages. Methods:Thirty male patients who were diagnosed with obstructive sleep apnea syndrome (OSAS) by polysomnography(PSG) were enrolled in the study. The RR intervals,sleep stages and relative data were extracted during the OA (Event),as well as a 15-second period before and after the OA(Pre-,Post-). Heart rate variability (HRV) parameters were calculated and classified in light sleep stage (S1~2) and REM. Then the influence of sleep stages on HRV was analyzed and compared. Results:RR-Mean and RR-SD shifted to the lowest and ΔRR-Mean turned to the highest with in both stage 1~2 and REM with OA,while the trends shifted back again after OA. However,RR-Mean in REM was lower than that in S1~2 during the whole process. Conclusion:Sleep stages and respiratory events lead to repeated changes of autonomic nervous system activity in patients with OSAS during sleep. The sympathetic activity dominates during REM and OA. These might be associated with the development of cardiovascular diseases in patients with OSAS.