This study investigates the connection of Obstructive Sleep Apnea (OSA) with the expression and daily oscillation patterns of core circadian clock genes and related genes. OSA, a sleep disorder characterized by repetitive airway occlusion leading to nocturnal arousals, sleep fragmentation, and intermittent hypoxemia (IH), shares sleep dysfunction as an overlapping phenotype with circadian clock genes. The research involved 40 subjects (30 OSA patients and 10 normal controls), categorized into four groups based on Polysomnography (PSG) results: normal, mild, moderate, and severe. Peripheral blood samples were collected twice from each participant in the evening before and the morning after PSG examination. Using real-time quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR), the study measured the expression levels of target genes in leukocytes. Results revealed changes in diurnal expression patterns of several genes (