Abstract: Xishuangbanna of China and Cambodia are both located in the same rive basin of Lanchang/Mekong River , the former is in the upper stream where belongs to the climate of northern tropics, and the latter is in the lower stream, where belongs to the climate of the tropics with a distance of some 1 000 km from north to south . Dai and Khmer are the major nationalities
of each state or region , they have used some 1 000 species of medicinal plants and accumulated plenty of traditional medical knowledge in the long historical developing process . The paper compares the similarities and differences of medicinal plants used by the two nationalities and their traditional medical knowledge in accordance of existing literture and the author′s field investigations . The results show that the similar index of common use medicinal plants between the two area is quite low which is 0 . 15 .Most of them are herbal and shrubby plants; the knowledge of medicinal plants accumulated by the two nationalities on the using parts, using styles and the main diseases treated are quite different , and each has his own strong points, which have closing relationship with the ecoenvironment, historical development , their ways of agricultural practise and lifestyle, and the effect of exotic cultures .

Key words: Medicinal plants