OBJECTIVE: To explore the influence of obstructive sleep apnea hypopnea syndrome (OSAHS) on endothelial function and autonomic modulation. METHODS: Electrocardiogram and beat-to-beat blood pressure from the radial artery were continuously recorded by polysomnography and applanation tonometry, respectively in OSAHS patients (OSAHS group, n=20) and obese controls (control group, n=20). Vascular endothelial function was evaluated by arterial augmentation index (AAI), and autonomic modulation was evaluated by heart rate variability (HRV) and blood pressure variability (BPV). RESULTS: The baseline AAI and BPV low frequency (LF) were significantly higher in OSAHS group than in control group (P<0.05). Compared with the pre-sleep levels, systolic blood pressure, diastolic blood pressure, HRV LF, HRV LF/high frequency and BPV LF significantly increased after over-night sleeps in OSAHS group (P<0.001), while HRV high frequency significantly decreased (P<0.05). CONCLUSION: OSAHS patients usually have endothelial dysfunction and autonomic modulation disorder, which are independently related with OSAHS.