The obstructive sleep apnea (OSA) primarily affects adult male and occurs in perhaps 1~4% of the adult population. The clinical syndrome is snoring, sleep fragmentation, sleep apnea, and excessive daytime sleepiness. For diagnosis of obstructive sleep apnea, history taking and physical examinations are needed. But the diagnosis of obstructive sleep apnea is confirmed by overnight sleep and respiratory monitoring such as polysomnography. Obstructive sleep apnea syndrome is defined as the groups with apnea index of above 5. There are many variable parameters in polysomnographic evaluation representing the manifestations of the sleep. So we have performed polysomnographic monitoring to 41 patients who visited our hospital with the symptoms of obstructive sleep apnea. We grouped the examinee into two groups according to the apnea index of 5. Group 1 is the control group with apnea index of less than 5. Group 2 is the patient's group with apnea index of equal or more than 5. The lowest oxygen saturation and maximal apnea time in polysomnographic monitoring was compared between the two groups to represent the difference of sleep manifestation. The body mass index and findings of EKG and PFT were compared to evaluate the clinical features of the obstructive sleep apnea. The results were as follows：1) The mean maximal apnea time was 31.7±25.2 sec in group 1 (A.I<5) and 78.5±95.5 sec in group 2 (A.I≤5) (p<0.05). 2) The mean lowest oxygen saturation was 90.4±9.7% in group 1 and 81.3±17.4 in group 2 (p<0.001). 3) The mean body mass index was 25.03±6.02 in group 1 and 26.98±6.58 in group 2 (p<0.1). 4) Abnormal cardiac rhythms were detected in 6 out of 16 persons (37%) in group 1, 16 out of 25 persons (64%) in group 2. 5) Abnormal PFT findings were detected in 1 out of 7 persons in group 1 (14%) and 5 out of 20 persons (25%).