Background and Objective: Obstructive Sleep Apnea (OSA) is strongly associated with Resistant Hypertension (RHT). Continuous positive airway pressure (CPAP) is the treatment of choice for moderate-severe OSA. Its benefit in terms of blood pressure (BP) control is still unclear. The objective of the study is to evaluate the effect of CPAP on BP in patients with RHT and moderate-severe OSA. Methods: This was a prospective intervention study that included 124 patients with RHT and moderate/severe OSA (AHI>15/hour) divided in 2 groups. Patients using CPAP uninterruptedly for a minimum period of 12 months (CPAP group) were compared with those who refused to use CPAP despite clinical indication (Control group). Office BP and 24-hour ABPM were obtained at baseline and after follow-up. Primary outcomes were changes in office and ambulatory BPs, and nocturnal BP reduction. Results: 124 individuals were included (37.9% male with a mean age of 60.7 ± 7.8 years), 65 in the CPAP group and 59 in the control group with a median [interquartile range] follow-up time of 68 [49-81] months. There was a reduction in office systolic BP (SBP) of -7.5 mmHg ([CI95%: -16.3 to -1.1],p=0.089), in nocturnal SBP and diastolic BP (DBP) of – 6.1 mmHg ([CI95%: -12.4 to 0.3],p=0.06) and -3.5 mmHg ([CI95%: -7.4 to 0.6],p=0.092), respectively, without reaching statistical significance. Otherwise, after excluding 9 patients of CPAP group with low adherence, we found a reduction in office SBP of -10.3 mmHg ([CI95%: -19.7 to 0.9],p=0.031), in 24-hour SBP and DBP of – 4.8 mmHg ([CI95%: -10.5 to 0.8],p=0.095) and -3.4 mmHg ([CI95%: -6.8 to 0.1],p=0.045), and in nocturnal SBP and DBP of – 8.1 mmHg ([CI95%: -14.7 to -1.5],p=0.017) and -5.3 mmHg ([CI95%: -9.6 to -1.1],p=0.014), respectively. Conclusion: Long term use of CPAP reduced office, 24-hour and nighttime SBP specially in resistant hypertensives with good CPAP adherence.