OBJECTIVES: This study aims to analyze the association between the severity of sleep apnea, sleep and mood related scales, and activity during sleep in obstructive sleep apnea syndrome (OSAS) patients. METHODS: One hundred seventy six drug-free male patients confirmed as OSAS (average age=43+/-11 years) were selected through nocturnal polysomnography (NPSG). OSAS was diagnosed with apnea-hypopnea index (AHI) >5, mean AHI was 39.6+/-26.0. Sleep related scales were Stanford Sleepiness Scale (SSS), Epworth Sleepiness Scale (ESS), Pittsburg Sleep Quality Index (PSQI) and Morningness-Eveningness Scale (MES). Mood related scales were Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), State-Trait Anxiety Inventory (STAI) I, II and Profile of Mood States (POMS). NPSG was performed overnight with both wrist actigraphy (WATG). Parameters produced from WATG were total activity score, mean activity score and fragmentation index. We analyzed the correlation between each scale, AHI scored from NPSG and activity score analyzed from WATG. RESULTS: ESS showed significant positive correlation with PSQI, BDI, BAI and STAI I, II, respectively (p<0.01). SSS showed significant positive correlation with PSQI and BAI (p<0.05, p<0.01). BAI showed significant positive correlation with total activity score, mean activity score and fragmentation index (p<0.05, p<0.01, p<0.05). Total activity score showed significant positive correlation with ESS and BAI, respectively (p<0.05). Fragmentation index showed significant positive correlation with ESS, PSQI and BAI (p<0.05, p<0.01, p<0.05). AHI, indicator of sleep apnea is showed no significant correlation with each sleep and mood related scale. CONCLUSION: The degree of daytime sleepiness tends to be associated with night sleep satisfaction, depression and anxiety, and the activity during sleep rather than the severity of sleep apnea.