The karyotype and the C-band patterns of the Baiji dolphin (Lipotes vexillifer) was performed on cultures of peripheral leukocytes. The chromosome number of diploid is 44 (2n=44). The karyotype was composed of 12M, 18SM, 4St, 8T and 2 sex chromosome. The largest autosome was ST1, and the smallest was T4. X chromosome was the largest in M group, and Y was the smallest in T group. The C-band heterochromatin was mainly present in the chromosome arm area as distinct blocks. The centromeric regions were faintly stained. The largest heterochromatic blocks were seen proximal to the middle of the long arms of the chromosome SM1, SM2, ST1 and ST2. The size heteromorphism was found in the terminal heterochromatic blocks of SM1, ST1 and in the interstitial of SM5, T1, T2. The C-heterochromatin approximated 12% of the total chromatin in one cell measured.