Introduction: Obstructive sleep apnea (OSA) occurs more predominantly during REM sleep (REM-OSA) compared to NREM sleep (NREM-OSA) in both children and adults. However, it is not clear whether REM-OSA and NREM-OSA are separate clinical phenotypes of OSA or represent 2 ends of OSA severity spectrum. Objective: We aimed to compare clinical and polysomnography (PSG) characteristics of REM-OSA versus NREM-OSA in children, and to evaluate the effect of these characteristics on REM-related over NREM-related obstructive AHI ratio (REM-OAHI/NREM-OAHI). Methods: This was a retrospective study. Clinical and PSG data of all children diagnosed by PSG with moderate to severe OSA between 2019-2024 were collected and analyzed. REM-OSA was defined as REM-OAHI/NREM-OAHI ratio of > 2. NREM-OSA was defined as REM-OAHI/NREM-OAHI of < 2. Results: A total of 253 patients (169 male and 84 female) met the inclusion criteria. REM-OSA was identified in 174 (68.7%) patients, and NREM-OSA in 79 (31.2%) patients. There was no significant difference between REM-OSA and NREM OSA groups in gender, BMI, clinical diagnosis, symptoms or oxygenation indices. However, REM-OSA group had lower OAHI and less severe OSA than NREM-OSA group (P=0.004, P= 0.003, respectively). Regression analysis showed that low OAHI was the only significant predictor of REM-OSA and the only predictor of high REM-AHI/NREM-AHI ratio, respectively (P=0.001, P=0.001). Conclusion: REM-OSA and NREM-OSA are not likely to be separate clinical phenotypes of OSA but only markers of its disease severity, with NREM-OSA indicating more severe disease.