Some ecological aspects of the common warthog (Phacochoerus africanus) were studiedrnfrom FebrllUlY 2000 to December 2000 in the Bale Mountains National Park (BMNP).rnData were collected on the poplilation estimate, age and sex categOlY, and diurnal activityrnpattern of the species by dividing the study period into d,y and wet seasons. Data werernanalyzed using SPSS compllter software package and compared using one-way ANOVArn(p=0.05) and t-test for independent sample of groups (p=0. 05). Both total and samplerncounts were used to estimate the population of warthogs in the study area. 576 animalsrnwere counted in the whole study area (536 in the dry season and 616 in the wet season).rnDllring counting, each individual in a group was identified into its respective age and sexrncategories. The result of the study showed a great percentage (>50%) of yo ling animals inrnthe populatioll. There is IIl1eqllal sex ratio in the population. Male to female ratio of thernpopulation shows 23.9 % more females than males. The relatively high percentage of yo lingrnindividuals and breeding females shows that warthog population in the study area isrnincreasing. The major activities of the species were feeding and lying down. The amoullt ofrnhOllrs devoted to each activity by Group I (all adult male) and Group II (a female with herrntwo hoglets) was not significantly different except feeding. The amount of time spent inrnfeeding is related to feeding efficiency based on the size of their mouths and molars.rnFeeding activity was intensive and reached its peak in the early morning and laternafternoon. Resting/lying dowlI increased in the middle of the day. The activity follows therngeneral pattern of ungulates in the Bale Moulltains National Park, characterized byrnmorning and evening activity with a period of rest in the middle of the day.