During June and July 2001,the incubation behavior with nest description of Hume's Leaf Warblers(Phylloscopus humei) was studied at the Lianhuashan Natural Reserve in Gansu Province of China.The clutch size was 4.3±0.5 eggs(4-5,n=4) with measurement of(14.0±0.4) mm×(11.2±0.4) mm(n=17).Nestling period was 13.8±0.5 d(13-14,n=4).Active length in the day of the female during the incubation period averaged 833.2±40.0 min.Female left the nest averaged 46.6±12.2 times(n=27) per day,and the duration of period-off and period-on were 5.3±2.8 min(n= 1 435) and(12.7±7.5) min(n= 1 409) respectively.Constancy of incubation was 72.4%±11.6%(n=21).The duration of the period-off and period-on in raining days was different from which in sunny days,the constancy of incubation in sunny day was 71.5%±12.1%(n=13) and which in raining days was 75.1%±9.0%(n=8).Egg temperature during all the incubation period averaged 31.2℃(58 879 recordings in 49 066 min),and the egg temperature decreased 9.4±3.4℃(n= 1 450) in average during period-off.