Studies on the species composition, relative abundance and distribution of medium and large mammals were carried out from August 2015 to July 2016 in Mengaza communal forest. Data were collected using line transect technique. A total of twelve species of medium and large mammals were identified and recorded in the study area. Rock hyrax (Procavia capensis), porcupine (Hystrix cristata), honey badger (Mellivera capensis), vervet monkey (Chlorocebus aethiops), Abyssinian hare (Lepus habessinicus), black backed jackal (Canis mesomelas), klipspringer (Oreotragus oreotragus), olive baboon (Papio anubis), were among the medium mammals but Spotted hyena (Crocuta crocuta), aardvark (Oryctropus afer), bohor reed buck (Redunca redunca) and common duiker (Sylvicapra grimmia) were among the large mammals identified in the study area. Olive baboon (32.7%) was the most abundant species during dry and wet seasons. Mammalian species composition between the two habitats (natural forest and plantation) was not significant ( χ2 = 0.47, df =1, P > 0.05). However, there was seasonal variation in the abundance of individuals of medium and large mammals ( χ2 = 3.89, df = 1, P < 0.05). The area is facing severe degradation due to human population pressure. Therefore, there should be proper conservation of the forest to sustain the wildlife species living there.