Study on diversity, relative abundance, and habitat association of medium and larger sized mammals was conducted in Tankara forest, western Ethiopia, from Jenuary 2019 up to June 2020. In this area mammals were directly relevant to local community as source of food, recreational values, source of economy and spirituals values (kallicha). Four habitat types (montane forest, riverine forest, shrubland, and grassland) were identified and sampled. Line transect method was implemented to record medium and large sized mammalian diversity. Accordingly, 6 line transects were used in data collection throughout the study area. Among these lines transects, two from montane, one from riverine, two from shrubland, and one from grassland. Direct and indirect observations were used for surveying of mammals. A total of 24 medium and large sized mammals were identified and recorded in the study area. Riverine forest was the habitat relatively with the most species diversity (H=2.669), and evenness (J=0.851) followed by montane forest (H=2.377) and evenness (J=0.793) and grassland habitat was considered as the habitat with the lowest diversity (H=2.162) and evenness (J=0.902). The relative abundance of different mammalian species varies in the study area. As a result, guereza (Colobus guereza) with 20.42%, grivet monkey (Chlorcebus aethiops) with 17.5%, Olive baboon (Papio anubis) with 12.5% were relatively the most abundant species Whereas Klipspringer (Oreotagusoreotagus) with 0.83%, honey badger (Mellivora capensis) with 0.83% were the least abundant species in study area. The highest species similarity (SI=0.883) of medium and large mammalian was recorded in riverine forest and montane forests habitats of Tankara forest, while the least species similarity (SI=0.516) of medium and large mammalian was recorded in grassland and shrubland. Many mammalian species were highly disturbed in Tankara forest due to anthropogenic factors. Therefore, all habitats of study area should be free from any human activities. The present study was provided awareness for the local community members about the significance of mammals and the actual benefits they provide if sustainable conservation strategies will be implemented in the study area. Key-word: Diversity, habitat association, mammals, relative abundance, Tankara forest.