Phia Oac - Phia Den Natural Protection Area belong to Nguyen Binh district, Cao Bang province which is located in the highland, terrain, forestry land area accounts for 84 percent of the total area in which mainly natural forest on the limestone. The study area includes the limestone mountain ranges with many high peaks, steep slope, average elevation 1160-l328m, gradient from 30 to 40°, some where over 45°. The components of rare and endangered plants in the study area is very diverse with 33 species, 27 genera and 20 families of the three branches of vascular plants named in the Vietnam Red Book, lUCN Red List. Especially, the first time the new distribution of a population of Xanthocyparis vietnamensis on the limestone mountains at elevations between 1285-l328m and populations of Paphiopedilum emersonii are identified and recorded, currently at critically endangered CR in the IUCN Red List that is distributed on limestone slopes at elevations between 1230-1278m. The results of this study is also identified 5 ecological and environmental factors impact to distribution of floristic in this area.