To investigate the composition and floristic diversity of one hectare of a dense forest on a terra firme oxisol plateau 90 km from the Manaus (02ÔøO35\"45\" S e 60ÔøO12\"40\" W) all trees lianas and palm trees with diameter at breast height (DBH) > 10 cm were inventoried along two parallel transects of 500 x 10 m. The landscape is vegetationally exuberant and homogeneous with a large quantity of tall slender trees. A total of 670 individuals in 48 families 133 genera and 245 species were registered in this floristic inventory. 467 of the plants sampled exhibited DBH < 22.1 cm representing 70% of the total. Abarema mataybifolia (Sandw.) Barneby & Grimes Leonia glycycarpa Ruiz & Pav. Swartzia reticulata Ducke and Aspidosperma oblongum A. DC. were the species with DBH > 90 cm. Families with greatest species richness and importance value were Fabaceae Sapotaceae and Lecythidaceae. The Shannon-Wiener diversity (H\" = 5.1) and evenness (E\" = 0.92) indices suggest that the forest environment is very diversified but with a relative uniformity of species. However a uniform spatial distribution of the species in this forest environment was not observed. According to Mantel\"s test (p < 0.001) the highest floristic similarity is a function of geographic proximity among suplots.