The study was carried out to assess the population size and distribution of diurnal large wild mammals in southern Great Rift Valley, Ethiopia. The study area was stratified into four habitat types; such as riverine forest, and ground-water forest, grassland, and bushland. Samples of animals were surveyed through the transect method. The total number of mammals belonging to the 15 different species was 1681 and 1245 during the wet and dry seasons. The Burchell’s zebra, Anubis baboon, Vervet monkey, and Grant’s gazelle were the most abundant species; while, Abyssinian hare and Bush duiker were the least abundant species. The highest mammalian species has been supported by the bushland habitat followed by open grassland, riverine forest, and ground-water forest in both seasons. Despite the park is home to various types of mammalian species, the management plan of the park should consider getting sustainable benefits from the mammalian species in the future.