Abstract:The dipterocarp forest of Xishuangbanna, with tropical Asian floristic element as its mainstay, undoubtedly belongs to tropical Asia flora in nature and acts as a part of northern margin of the latter. The forest, especially the part of tree layers, has the same family composition as dipterocarp forests of tropical Asia and most of its genera are shared by the latter and so the forest can be floristically classified as a type of the latter. As occuring at the northern margin of tropical zone of SE Asia, the flora of the forest is characterized by the merging of tropical Asian floristic element into subtropical floristic element of S China and is however transitional towards the forest flora of S China.