The aim of this study is to assess the state of plant biodiversity in the natural rangelands of transhumant cattle herds in the Classified Forest of Upper Alibori (CFUA), Northern Benin. Forty-five (45) phytosociological plots were carried out using the Braun-Blanquet method. The phytosociological data were submitted to Detrended Correspondence Analysis (DCA) under the software R.3.3.2 with a package vegan. The results revealed that the natural rangelands of the CFUA have 178 species belonging to 45 families of which the most abundant and dominant are the Poaceae, Caesalpiniaceae, Combretaceae and Rubiaceae. Three (3) types of pasture were highlighted: Detarium microcarpum and Pennisetum polystachion ; Isoberlinia doka and Brachiaria stigmatisata; Prosopis africana and Pennisetum pedicellatum. The most abundant and dominant biological types on these natural rangelands are phanerophytes followed by therophytes. However, Sudanese species are the most abundant and dominant. This shows that pastures in this protected area are relatively undisturbed. The unsweetened and invasive species such as Senna obtusifolia, Hyptis suaveolens, Loudetia togoensis, etc. were also observed in this natural rangeland. It follows from this study that the natural rangelands of CFUA are degraded due to the strong agropastoral pressure.