Objective:To investigate the efficacy and possible mechanism of continuous positive airway pressure(CPAP) treatment on blood pressure in patients with obstructive sleep syndrome(OSAS) and resistant hypertension(RH). Methods:Thirteen OSAS patients with RH were recruited. Before and on three months’ CPAP treatment,their blood pressures at 10:00 PM,2:00 AM and 6:00 AM were measured,and their morning plasma concentrations of aldosterone(ALD) and plasma renin activity(PRA) were tested at supine position with radioimmonoassay. Results:Compared with blood pressure before CPAP treatment,there was a significant decrease in blood pressure after three months’ CPAP treatment(all P < 0.01). Comparison of plasma concentrations of ALD and PRA before and after three months’ CPAP treatment indicated that there was a significant difference in ALD[(195.5 ± 15.1)ng/L vs (148.3 ± 19.4)ng/L,P < 0.01] but not significantly different in PRA[(0.20 ± 0.12)μg/L·h vs(0.27 ± 0.14)μg/L·h,P = 0.221]. Conclusion:CPAP treatment could significantly improve RH and plasma ALD concentration. Plasma ALD concentration elevating was possibly involved in pathogenesis of RH in OSAS patients.