This thesis studied on characteristics of chromosomal banded karyotype of two dolphin species (Lipotes vexilifer and Neophocaena phocaenoides), which lived in the Changjiang River in China, and compared them with those of some other cetacean species. The result might be briefly summarized as follows: (1) The karyotype of Lipotes was 2n = 44, xy (♂: 13m +18sm + 4st + 9t) , and the karyotypeof Neophocaena was 2n = 44, xy (♂: 11m + 20sm + 4st + 9t). There was only one pair of Ag-NOR sit existing on the smallest pair chromosomes of Lipotes and association of the pair has been observed in early mitosis metaphase, which was the same as that of Neophocaena and some other cetaceans whose chromosome numbers were 2n = 44. Only one silver stained nucleolus was observed in intermitotic nucleus. (2) The number of G-band of Lipotes was about 160, its distribution was similar to Balaenoptera borealis of suborder Mysticeti. But the number of G-banded of Neophocaena was 140 or so, and its distribution was much similar to Stenella dubia of suborder Odontoceti. Basing on these results, the origin of cetaceans was preliminarily discussed. (3) By firstly applying the latest technology of restriction endonuclease C-band of Lipotes was successfully induced with Hae. The results were similar with that of normal C-banded technology. C-band of Neophocaena was also induced in st1, st2 and t1 chromosomal pairs with restriction endonuclease AluI, its distribution was the same as the results by using normal C-banded technology. This work supplied a new method for cytogenetic studies on cetaceans. The thesis also investigated the Tm value and base composition of nuclear DNA of Lipotes by using thermal denaturation method. From differential melting rate profiles of Lipotes, it was found that heterogeneity of base composition of Lipotes was relatively high, and there existed many GC-rich DNA sequences.