Abstract: AIM: To investigate the characteristics and level of renin-angiotensin II-aldosterone system in hypertensive patients with obstructive sleep apnea-hypopnea syndrome (OSAHS). METHODS: Ninety-six hypertensive inpatients with OSAHS were included for polysomnography and quantitative analysis of plasma level of renin, angiotensin II and aldosterone. All subjects were divided into two groups based on the apnea-hypopnea index (AHI), one mild group with 46 cases and the other moderate-to severe group with 50 cases. Comparison of serum level of renin, angiotensin II and aldosterone was made between groups. All the above three parameters were compared among all included subjects based on age stratification. RESULTS: No significant difference in serum level of renin and angiotensin II was found between groups, whereas a significant difference was observed in aldosterone level ［(211±85) ng/L vs. (175±58) ng/L, P<0.05］. Significantly higher serum level of aldosterone and lower level of renin were found in hypertensive patients with OSAHS compared with those with simple hypertension based on age stratification (P<0.01). CONCLUSION: Serum level of aldosterone is significantly elevated in hypertensive patients with OASHS and serum levels of renin and aldosterone are also significantly higher than those of patients with simple hypertension.