Abstract: To understand the characteristics, occurrence and evolution of the flora of a given region, endemism has become a flora and biodiversity research field of interest. The Nu River, also known as the Salween River, is one of the most important rivers in southwest China, but little is known about the flora of Nu River Valley. We conducted a preliminary investigation on seed plants between the southern tip of the Sino-Burmese border (Mucheng) and the Yunnan-Tibet border region (Qiunatong) of Nu River Valley from March to October, 2013. Both quadrat investigation and line transects were used in our field survey. We found 1718 seed plants species belonging to 776 genera and 164 families in Nu River Valley of Yunnan. Among them, four families were endemic to East Asia, and one genera and 316 species were endemic to China, of which 68 species were found in Yunnan (including three species to Nu River Valley). The endemism in the familial rank indicated that the flora of this region belonged to the East Asian flora, but no evident endemism in regards to genera rank was found. The Chinese endemic species had close relationships to the flora of northwestern and southwestern Yunnan, southern and southwestern China, and the Sino-Himalaya Region of East Asia.