The Ruvubu National Park, the biggest protected area and biodiversity refuge of the country, is comparatively less studied than western Burundi near Bujumbura, the capital. This article reports the results of a botanical inventory of the vascular plants from the protected area, evidences species newly encountered and establishes a comparison of the floristic diversity with the Akagera National Park in Rwanda located in the same phytochorion, in the Lake Victoria regional mosaic. Records from the Ruvubu include 522 species (including infraspecific groups) from 96 families and 306 genera, representing nearly 17% of the known vascular plants of Burundi. The most common families were the Fabaceae, the Asteraceae and the Poaceae. 96 species or 18% of the flora were encountered for the first time in the park. Study of environmental determinants of Leguminosae abundance and floristic variability would provide more precisions.