A binational checklist of the mammal fauna from the Orinoco river basin is consolidated, reporting 318 species distributed across 12 orders, 40 families and 156 genera. This diversity represents the 76,8 % of the mammal species of Venezuela and the 68,7 % of Colombia. The order Chiroptera is the more representative with 150 species (47,5 %) followed by rodents with 77 species (24,4 %). The Guayana region is the more diverse while Deltaic region has the lowest richness value. The endangered categories considered by UICN and the Colombian and Venezuelan red books show that field work as well as deeper taxonomic and ecological research are essential for the widening of the mammal species distribution knowledge and conservation planning of priority areas for the Orinoco basin.