Abstract: From March,1987 to June,1988 we worked on the fasting endurance and loss of energy materials at night of Pycnonotus xanthorrhous in Kunming,Yunan,China.P.xanthorrhous is a common and resident species in Yunan.Kunming is in the southwest of China (24°23′-25°36′N,102°14′-103°03′E).The seasonal changes is small.The paper reports the fasting endurance of P.xanthorrhous was 19 hours.When they died,the reserve of fat declined 79%,the non-fat flight muscle declined 46%,and the sugar of liver declined 96%.At night P.xanthorrhous lost the great amount of fat reserve,especially exhausted the highest percent lipeds at the night of winter.The energy provived by sugar of liver was very little.During breeding and moulting period,the flight muscle lost the great amount of protein reserve at night to supply the needs of birds.