The result of the study on the effects livestock grazing on the diet and behavioral ecology of the geladas in the SMNP is presented in this thesis. The study was aimed to investigate the behavioral responses of geladas to livestock grazing area of the SMNP. The study was carried out from February 2019 to July 2019 including the dry and wet seasons. A 25 m transect across the grazing category was laid down. Along the transect line five temporary sample plots were established (1m2 ). For aboveground biomass estimation, grass and forbs were clipped from 0.25m2 in every sample plot, and belowground biomass were estimated from two soil cores (diameter = 6.35 cm, depth =20 cm) from all transects. Behavioral data were collected using scan sampling in 15 minutes intervals. The effects of livestock grazing on activity time budgets were statistically analyzed by MANCOVA. Daily range length and home range size were estimated using Open Jump toolbox (MOVEAN), and statistically tested by Mann-Whitney U test. A total of 46 plant species within 21 families were identified over the study period. Above and belowground biomass were significantly varied across grazing levels (F[4, 1] = 782.68, P = 0.027). From 3427 behavioral scans on the various activities, feeding was the most frequent behavioral activity followed by moving, accounting about 43.04% and 38.06% of the time respectively. The study revealed that grazing has a statistically significant effect on the overall activity time budgets. The study provides that geladas foraged on 24 different species of plants. However, only few plant species had significant proportion on the diet of geladas. 70.82% of their diets were taken from four species of grasses. Furthermore, geladas adjust their ranging length and home range in response to grazing intensity. The study suggests that livestock grazing has been affecting the quality of habitat and food availability to geladas. Therefore, livestock grazing should be reduced in the home range of the geladas. Keywords/phrases: activity time, biomass, diet, feeding ecology, gelada, ranging behavior, SMNP 1 1. INTRODUCTION 1.1.Background of the Study Ethiopia is renowned for its endemic fauna and flora, which arise from the vast extent and isolation of its highlands within the Afrotropical region. The country possess the largest extent of Afroalpine and sub-afro-alpine habitats in Africa (Stephens et al., 2001). Ethiopia is a home for a diverse flora and fauna including more than 320 species of mammals (Afework Bekele and Yalden, 2013; Lavrenchenko and Afework Bekle, 2017). Among the mammals of Ethiopia, around 30 species and sub species are non-human primates (Grubb et al., 20