Abstract: White-cheeked gibbon (H.leucogenys) is distributed in the south of Yunnan,China.The chromosomes of a female and a male were studied by several banding techniques (G-,C- and Ag-staining),and a techniqe for simultaneous exhibiting chromosome replication patterns and late replicating Y chromosome.The diploid chromosome number is 52.There are 22 pairs of metacentrics or submetacentrics (Nos.1-22 );3 pairs of acrocentrics(Nos.23-25),and chromosomes Nos.23-24 with a secondary constriction near the centromere on the short arm.The X chromosome is a large metacentric,and the Y,the smallest acrocentric.Its karyotype formula is 44(M or SM)+6(A),XY(M,A).The centrimeric distribution of heterochromatin has been demonstrated in some chromosomes.In addion,there are 3 kinds of heterochromatin on the chromosomes:(1) absent of centromeric heterochromatin,(2) interstitial heterochromatin,(3) terminal heterochromatin.Interstitial heterochromatin has been observed on the biarm of X chromosome.Y chromosome is completely C-band positive.Silver staining revealed 5 chromosomes with NORs in the male specimen.4 Ag-NORs of them are located on the secondary constriction of chromosomes 23 and 24 respectively,and one of them is located on the Y chromosome which has been confirmed by Fluorescence in situ hybridization (FISH) in the same cell.There are 4 chromosomes with Ag-NORs in the female specimen,and they are also located on the secondary constriction of chromosomes 23 and 24.Moreover,the association of Ag-NORs have been observed.Base on the above results,the relationship in gibbons and the way of chromosome evolution in the genus Hylobates have been discussed.