Abstract: There are 239 species belonging to 25 families and 124 genera of freshwater fishes in the Zhujiang River (Pearl R.) system. Among them are 146 species, or 61.1% of the total, of cyprinids, 23 species, or 9.6% of cobitids, and 22 species, or 9.2%, of homalopterids. Apparently, cyprinoid species constitute the main component of the fish fauna. In comparison cyprinid fishes of the Zhujiang with those of the Chang Jiang (the River Yangtze), the relative proportions of Cultrinae, Leuciscinae, Acheilognathinae and Gobioninae in the former are smaller, whereas those of Danioninae and Labeoninae are larger. The situation is reversed when the ichthyofauna of the Zhujiang River system is compared with that of the Red River and the Mekong River. Thus, it demonstrates a faunal succession from the north to the south.Among the fishes of the Zhujiang River, there is scarcity of endemic genera and no endemic family, yet many endemic species are present. In that river, 127 species or 53.2% of the total have not hitherto been reported from the Chang Jiang River. Accordingly, Mori (1936) takes the Nanling Mountain Range, the watershed dividing the two rivers, as the demarcation line between Palaearctic Region and Oriental Region, and Li Sizhong (1981) shares this viewpoint.Dealing with the ichthyofanna, we are of the opinion that the difference between fishes in two areas is a universal phenomenon and, hence, a simple comparision of their overall similarity is inadequate or even misleading for formal division. The formation of a contain zoogeographical division unit is surely related to a definite geological event in a given geological period. Difference of fish composition caused by other historical factors before or after such a period bears no significance for the zoogeraphical division. Only the element which has a direct relation to such geological event can be used as the mark of the division. Moreover, the higher the level of zoogeographical division, the more ancient and the more important geological activities are to be related with. For iustance, the division of Arctogaea and Notogaea is related to the separation of Gondwanaland and the close of Tethys Sea in Cretaceous Period, and is marked by the arising and the distribution of Placentalia. The division of Holarctic Region and Oriental Region is related to the temperature decrease that occurred in the middle stage of Tertiary Period and the fauna difference bearing direct relation to this event can only be considered as indicative of that division. Speaking out the freshwater fish fauna in East. Asia, the global temperature decrease caused the extinction of the primitive danionine and barbine fishes in the north, and as a result of adaptation, caused the evolution of Phoxinus, Leuciscus and some endemic genera of Leuciscinae in Europe and North America, as well as the genus Gobio of Gobioninae. At the same time, it resulted in the southward extention of some coldwater fishes such as salmonid fishes, which originally inhabited around the Arctic Ocean. In the south, fallowing the formation of rapid current at the primary stage of the uplift of the Xizang (Tibetan) Plateau, warm-water stream fishes such as Homalopteridae, Sisoridae, Amblycipitidae and Labeoninae of Cyprinidae arose. These two components shenld be the real mark for the division of the Holarctie and the Oriental Regions. Their natural distribution boundary is not the Nanling Mountain Range of South China, but the Qinling Mountain Range of Central China. Therefore, we consider that the Qinling Mountain Range should be the demarcation line between Horarctic Region and Oriental Region in East Asia.During the late Tertiary Period, owing to the monsoon climate caused by the uplift of the Xizang Plateau, a special fish-fauna including Cultrinae, Hypophthalmichthinae, Acheilognathinae, and some genera of Leuciseinae and Gobioninae of Cyprinidae came into being in the river plains of East Asia. These faunal compositions occurred relatively late in time and were relatively narrow in distribution, so that they can only be used as the basis of division on a lower level. These compositions dispersed southwards and were stopped by the Yunnan Plateau uplifted Miocene Epoch, arriving at neither the West River source of the Zhujiang River nor the upper reaches of the Red River. Therefore, along the eastern border of the Yunnan Plateau we can divide the Oriental Region into the South Asiatic Subregion and the South-east Asiatic Subregion. There are about 50 species in the upper reaches of the West River, lying in the South Asiatic Subregion, and only 22% of them are common to ther regions of the Zhujiang River lying in the South-east Asiatic Subregion.The Zhujiang River is located in subtropical karst region. Its complex environment resulted in fairly active speciation. This is the main reason of the difference between fish-fauna of the Chang Jiang River and that of the Zhujiang River. Such difference is comparatively local in extent and occurred relatively late in geological chronology, so the Nanling Mountain Range can serve as the boundary of zoogeographical divisions only on a relatively lower level.