Abstract： OBJECTIVE To investigate the polysomnographic differences between males and females with obstructive sleep apnea syndrome(OSAS).METHODS Adults visited to Beijing Tongren Hospital for sleep snoring from January 2023 to August 2023 who completed overnight polysomnography(PSG)and whose apnea hypopnea index(AHI)≥5 times/h were diagnosed as OSAS patients in this study.The general information,respiratory events and sleep structure were compared between male and female OSAS patients.RESULTS A total of 380 patients were included in this study with 293 males(77.1%)and 87 females(22.9%).Mean age was(44.4±11.5)years,and the mean body mass index was(26.5±3.9)kg/m2;AHI ranged between 5.0 and 115.8 times/h with a mean of(34.9±24.8)times/h;lowest oxygen saturation(LSpO2)ranged between 43%-97%with a mean of(80.7±11.6)%.Between male and female OSAS patients,the AHI in males was higher than females[(37.9±24.8)times/h vs.(24.5±21.7)times/h,P=0.000],and the AHI in REM was higher in males than females[(36.7±23.2)times/h vs.(30.9±22.8)times/h,P=0.040].LSpO2 was lower in males than females[(79.2±12.0)%vs.(85.7±8.3)%,P=0.000].There were significant differences for arousal index,sleep efficiency,N1 sleep percent and N3 sleep percent between two groups.Between male and female OSAS patients over 50 years old,AHI was still higher in males than in females[(39.3±21.4)times/h vs.(30.5±23.0)times/h,P=0.029],and there was no significant difference in AHIREM and LSpO2.The difference in sleep structure between male and female OSAS patients over 50 years old was consistent with that of participants.CONCLUSION The AHI and LSpO2 of male OSAS patients were more serious than those of female OSAS patients,and the reduction of slow wave sleep was more obvious.OSAS became worse after menopause,which was highlighted by the increase of respiratory events in REM and the more serious decline of LSpO2.The protective effect of female hormones on OSAS is mainly to alleviate REM respiratory events and hypoxia damage,rather than improving sleep structure.