Population estimate of grivet monkeys (Chlorocebus aethiops) and assessing the human-grivet monkey conflict is important for conserving the species in their natural habitat. The main objective of the present study was to determine population size of grivet monkeys and assess the degree of conflict between human and grivet monkeys in Alemsaga forest. Census of the population size of grivet monkeys was made using total counting from March to June 2023. Data about the human grivet monkey conflict was collected using structured questionnaire, and interview the experts, and focus group discussion. Desscriptive data was analyzed and presented the frequency, percentage and mean. Data were tested using using Chi-square test (p<0.05). Qualitative data was used to strengthen the quantitative data based on research questions. Significant difference in distribution of the grivet monkeys among the blocks .where Ambo Beras (block 4) was the most populated,while Aba-Libanos (block 5) was the least populated. The results indicated that the average population size of the grivet monkeys was 1368 individuals with Standard deviation is approximately 97.25. Significantly, higher mean population was recorded during the dry seasons, 1451 comapred to the wet seasons 1285.5 (χ2 = 10.01, df=1, P<0.05). The juvenile was the most dominant age group 624 (46%) followed by adult female 347 (25%), infants 254 (19%) and adult male 143(10%). The sex ratio of adult male to adult female was 1:2.43 and age ratio of infant to adult female was 1:1.37. The questionnaire survey indicated that there was moderate level of conflict between human and grivet monkeys, where the common cause of conflict was crop raiding by grivet monkeys and habitat destruction by humans. Barley and maize were the two most affected crops during both dry and wet seasons. The third preference crop for grivet monkeys was wheat was the third highest damaged crop during wet season but bean in the dry season. The people found adjacent to the forest were develop negative attitude towards grivet monkey probably due to the loss of crops by the monkeys. Hence, there is a need to create awareness to the local people on the ecological value of wildlife and eco-tourism so that both monkeys and humans can co-exist together by minimizing coflict.