Résumé : The assessment of species diversity remains an indispensable tool in the development of biodiversity conservation strategies and ecosystem management. In tropical rainforest, richness and species diversity are almost always high but they vary spatially. Several studies have been conducted at the local level to assess the richness and floristic composition of the forests of the Congolese central basin. With a hundred of inventory plots we performed in four forest sites in northeastern Congo Basin, we have shown that tree stands have significant variations in species diversity and species composition. The northern sites in Ituri and Rubi-Tele are less diverse than those of Yoko and Uma around Kisangani.