Between March 2005 and February 2006 we surveyed the large and medium sized mammals ( > 5 kg) of Arawale National Reserve, NE Kenya. Twenty-three mammal species were counted during the period, using ground transects. This included eight species listed in the 2008 IUCN Red List of Threatened Species. Densities and biomass of the larger mammals in the Reserve were generally low as compared to other protected areas in East Africa. There were no seasonal differences in the number of mammals counted, but differences between habitats were highly significant. Despite the low mammal densities, Arawale National Reserve is important for the conservation of threatened species, especially hirola Beatragus hunteri and wild dog Lycaon pictus.