Abstract: Vocalization is lesser apes very prominent behavior,which is important when applied in the survey and conservation monitoring.Based on a field work in West Yunnan,this paper presents the timing characteristics of hoolock gibbon (Hylobates hoolock) songs and its comparison with other populations studied and with other species,especially black gibbons.The hoolock songs occurred mostly before 12:00 in the morning,but some in the afternoon.Most songs occurred around the time of 09:05 (SD=109.5,n=68,range 07:12-16:30).The average duration of the songs was 19.7 min (SD=9.34,n=55,range 4-50).The gibbons started to call at different times in different seasons,possibly correlated with the dawn time.Among different sites,the starting time was of no clear difference.Usually gibbons called late when it was rainy,especially in wet season.The song starting time showed significant difference between wet season and dry season.The song duration showed significant difference between different sites at the same season.The timing of hoolock gibbons showed time (season)-specific characteristics,which might correlate with the dawning time or more exactly with the light tense.The habitat quality,group density and human disturbance wowld influence the singing frequency of days and times but with no determined relationships.The comparison between hoolock and black gibbons showed that hoolock song had a longer duration and a wider range of the time distribution,with significant difference.