Abstract: In the south-east and south Xizang, in cluding Medog, Zayü some western separate valleys Yadong, Kama near Zentang in Dinggye, Boqu near Zham in Nyalam and Gyirong, a mild climate prevails because of the very high mountains and the very deep valleys. According to our preliminary survey, 4/5 of the genera and 7/10 of the species, i.e. approximately representing all families and genera of the tropical and subtropical bryofliora of Xizang, are restricted to these localities below the altitude of 2,300 meters. It almost agrees with the previous presumption that the Tsangpo gorge is the line of connection between two paleoeontinents—Laurasia and Gondwana. Moreover, the bryoflora of these localities, besides the Indo-Malasian elements and East Asian elements as the main components, has at least about 40 genera in common with south America, Australia and Africa. According to the historical phytogeographical point of view, the distribution range of centain genera is formed through a period of long historical development. The same is true for the area of different species, although they are found in widely separate areas right now, yet they might have once a continuous distribution in certain historical age. The Indian plate collided against the eastern part of Laurasia and afterwards the Australasian plate moved to the north. All these might have dispersed the Gondwana elements as far as to the southeastern part of Xizang. It is very interesting to note that of the 32 genera of bryophytes endemic to East Asia, 13 have recently been found in the southeast and south Xizang and also in the neighbouring regions, i.e. Yunnan, Sichuan, where there are many genera being in common with southeast and south Xizang and also highly concentrated in distribution. This may suggest that the Himalayas, being the highest and youngest mountain range, have changed the atmospheric circulation, and have created a new ecological condition between tropical and frigid zones, which have given the distribution of the newly formed genera a suitable circumstance to survive. It may be presumed that the region covering counties Medog, Zayü, Yadong etc. in southeastern and southern parts of the Himalayas is a new center of distribution of bryophytes under the influence of the up-heaval of the Himalayas.