Objective:To investigate the effects of upper airway obstruction sites on polysomnographic parameters and clinical manifestations in patients with obstructive sleep apnea syndrome(OSAS). Methods:Thirty-six adult male OSAS patients with their AHI between 30~40 were selected to undergo overnight PSG test and simultaneous pressure measurement of upper airway and esophagus for identification of the lowest upper airway obstruction sites. Comparison was made among different obstruction sites(sites of soft palate,tongue-base and lower pharynx) for the following parameters:nocturnal mean arterial oxyhemoglobin saturation(meanSaO2) and minimal SpO2(miniSaO2),the longest obstructive apnea event time,rate of fall of SaO2(dSaO2/dt),arousal index; as well as some clinical manifestations:day-time epworth sleepiness scale,systolic blood pressure(SBp) at 9:00PM/SBp at 6:00AM,diastolic blood pressure(DBp) at 9:00PM/DBp at 6:00AM and incidences of hypertension. Results:There was no significant difference of mean SaO2,the longest obstructive apnea event time and SBp at 9:00PM/SBp at 6:00AM(P > 0.05) among three different lowest obstruction sites in OSAS patients. However,compared with the obstructive site at palate,the obstruction sites at tongue-base and lower pharynx displayed significant difference in the following PSG and clinical parameters:①lower miniSaO2(P < 0.05);②higher dSaO2/dt(P < 0.05); ③ higher arousal index and day-time epworth sleepiness scale(P < 0.01),lower DBp at 9:00PM/DBp at 6:00AM. (P < 0.05);④higher incidence of miniSaO2 < 80% and hypertension(all P < 0.01). Conclusion:In OSAS patients with similar AHI,the lowest upper airway obstruction site at tongue-base or lower pharnx may cause transcient hypoxiemia more efficiently and significantly as well as more severe clinical manifestations than the obstruction site at palate or higher.