Abstract Background and Aims Obstructive Sleep Apnea Syndrome (OSA) is common among CKD, in particular dialysis patients. However, it is not yet studied in a large polysomnography (PSG) database. Randomized controlled trials (RCTs) proved the effectiveness of continuous positive airway pressure (CPAP) for the SAS-related symptoms, but not for lowering the mortality risk of all-cause and cardiovascular disease. However, the effect of CPAP on mortality risk is not examined among dialysis patents. Method We identified dialysis patients by reviewing medical records in the Okinawa Nakamura Clinic (ONSLEEP). (J Clin Sleep Med 2021). In the ONSLEEP, a total of 10,856 Japanese patients received PSG from September 1990 to December 2010. We defined patients who were on CPAP more than one month as CPAP user. Patients qualified and eligible for CPAP but refused it were assigned as CPAP non-users. Median observation was 6.6 years. We studied 9,841 PSG patients after excluding those with insufficient data, age<20 years, and central SAS. Among them, we found 195 dialysis patients: 16 (1.0%) dialysis patients with AHI<5/hour in 1,665 subjects and 164 (2.5%) in 8,176 OSA patients. Mortality rate was compared between CPAP users and nonusers by multivariate logistic analysis adjusted for age, gender, body mass index (BMI), and apnea hypopnea index (AHI). Results Among the OSA dialysis patients (men 127, women 37), there were 116 (2.6%) in the CPAP users and 48 (2.2%) in the CPAP non-users, respectively. Number of deaths was 65 (39 CPAP users, 26 CPAP non-users) during the follow-up. The death rate was 33.6% in the CPAP users and 54.2% in the CPAP non-users, respectively. CPAP users showed better survival after starting dialysis; hazard ratio (HR) 0.52 and 95% confidence interval (CI) of 0.31 to 0.88 (P = 0.015). Age was also a significant predictor of death; HR (95% CI) 1.04 (1.02-1.06, P < 0.0001). Conclusion Dialysis patients with OSA showed better survival by use of CPAP. In dialysis patients, screening of OSA is recommended if they complained sleep problems such as insomnia, daytime sleepiness, headache, and fatigue. Also, we need further study for those CPAP nonusers.