Gelada baboon (Theropithecus gelada) belongs to one of the few primate genera endemic tornEthiopia. Theropithecus gelada is the only living species of its genus. The present research wasrnconducted from August 2010 to May 2011 to determine the habitat preference, population size,rnfeeding ecology, distribution pattern, activity and ranging patterns of the gelada baboon subspeciesrn(Theropithecus gelada unnamed sub-species), in Indato cliff, eastern Arsi, Ethiopia.rnVegetation composition in the home range was determined by quadrat sampling method. Thernactivity pattern, feeding ecology and ranging behaviour were studied with 15 minutes intervalrnscan sampling. The population size of the geladas was determined from total (direct) count. Arntotal of 529 individuals were recorded with a density of 0.34 gelada baboon/km2. Feedingrncomprised the major activity (41.73%), followed by moving (20.27%), resting (18.98%),rngrooming (9.2%), playing (5.1%), aggression (3.26%), sexual activity (1.43%) and drinkingrn(0.03%). Adult females spend 45.77% of the time feeding and 15.71% of their time resting.rnAdult males spend 39.23% of their time feeding and 29.21% through resting. The overall dietrncomposition of gelada baboon was dominated by short grass blades contributing to 34.87%.rnGrass roots and long grass blades made the second and third largest portion of the overall diet ofrngelada baboons at 25.24% and 18.67%, respectively. Gelada baboon also consumed unidentifiedrntubers (7.54%), herb leaves (7.30%), others (3.01%), herb roots (1.69%) and corms (1.67%).rnGelada baboon consumed a total of 10 plant species which accounted for 100% of their diet overrnthe course of the study period. Of these, the top four accounted for 97.21% of their overall diet.rnJaldoo (Hyparrhenia sp) contributed 49.37% and Qarasoo (Hyparrhenia hirta) contributedrn38.11% of their diet. The mean daily range length for the study troop was 1004.6 m and thernaverage home range size was 4.91km2. The narrow ecological niche of the species may be arnthreat for its survival due to grazing by cattle. Appropriate management action should be taken tornconserve the species and their most important food resources.rnKey words: Activity, diet, Gelada baboon, home range, Indato Forest, population size