Abstract: Objective To explore the effect of arousal parameters on excessive daytime sleepiness (EDS) in patients with obstructive sleep apnea syndrome (OSAS).Methods A total of 205 patients who underwent polysomnography (PSG) from June 2012 to September 2013 in our hospital were enrolled.They were divided into 3 groups:85 patients in the OSAS sleepiness group (AHI≥5/h,ESS≥9),86 patients in the OSAS non-sleepiness group (AHI ≥ 5/h,ESS < 9),and 34 healthy subjects in the control group (AHI < 5 times/h,ESS < 9).Patient characteristics and PSG parameters of the 3 groups were analyzed.Results The difference of age,BMI,ESS,N1 + N2%,N3%,AHI,oxygen desaturation index (ODI),mean oxygen saturation (MSaO2),lowest oxygen saturation (LSaO2),oxygen below 90% of the time (T90%),total arousal index (ARtotI),respiratory arousal index/ARtotI (RAI/ARtotI),spontaneous arousal index/ARtotI (SAI/ARtotI),sleep pressure score (SPS) were statistically different among the 3 groups(P<0.05).But except for REM% [(15 ±5)%,(16 ±6)%,(17 ±7)%,P >0.05],the difference of age and BMI between OSAS sleepiness group and OSAS non-sleepiness group were not significant(P > 0.016 7),but the difference of other indices between any 2 groups were significant (P < 0.016 7).ARtotI and SPS were positively correlated with ESS (r =0.383 and 0.244,P < 0.001).Logistic regression analysis showed that only awakening and SPS were the risk factors for OSAS [OR =1.070 (95% CI:1.038-1.102) and 0.158 (95% CI:0.026-0.984),respeetively].Conclusions Arousal at night is closely associated with EDS in OSAS.ARtotI and SPS can be evaluated as an objective indicator of EDS in OSAS patients.