Purpose: Although we spend about one-third of our lives in sleep and recognize its necessity for good health, sleep has only been partially elucidated in the last century. The nasal cycle of congestion and decongestion during sleep has various effects on human physiology. The aim of the present study was to investigate the effect of unilateral forced nostril breathing on sleep. Methods: Twenty-one healthy male volunteers aged 18-24 years were included in the study. Only individuals with right-hand dominance were included. Subjects were observed during sleep for three nights under different conditions: no obstruction (normal sleep) on the first night, right nasal obstruction on the second night, and left nasal obstruction on the third night.Results: The main findings of our study are that sleep efficiency, NREM stage III, and total sleep duration were greater during left nasal obstruction (right nostril dominant respiration), while apnea-hypopnea index (AHI), frequency of periodic limb movements, and oxygen desaturation were higher during right nasal obstruction (left nostril dominant respiration).Conclusion: The nasal cycle has a significant impact on sleep which is reflected in sleep recordings. Our result supports that nasal obstructions, due to deviations, concha hypertrophy, or congestion/decongestion, might affect the physiology of respiration and sleep. Nasal obstruction should be taken into consideration when evaluating patients in sleep laboratories and further studies are required to elucidate the situation in the patients with nasal obstruction.