Introduction: Acute malnutrition is a nutritional deficiency that results either from inadequate energy or protein intake. It is more prevalent in low-and middle-income countries. Even though efforts have been carried out at the global and national level, the burden is still intolerable and it attracts the attention of the government and researchers. Hence, this study aims to assess the magnitude of acute malnutrition and its associated factors among under-five children who attended Hamusit Health Centre from 1st September to 30th January 2021. Materials and methods: This institution-based cross-sectional study was conducted from 1st September to 30th January on 404 randomly selected under-five children who visited the health centre. Samples were selected using a simple random sampling technique, and the data were obtained using a pre-tested standardized questionnaire. For data entry and analysis, Epi-info 7 and SPSS 21 applications were used, respectively. Bivariable and multivariable binary logistic regression were used to identify associated factors at a 95% confidence interval. Significance was considered at p-value<0.05. Results: The present research involved a total of 404 children aged 6-59 months. The magnitude of acute malnutrition in this study was 14.4%. Children aged 6-23 months [AOR: 2.92; 95%CI (1.46, 5.85)], vitamin A supplementation [AOR: 0.49; 95%CI (0.25, 0.95)], not timely initiation of complementary feeding [AOR: 2.02; 95%CI (1.06, 3.82)] and children with diarrhea prior to two weeks of the survey [AOR: 2.47; 95% CI (1.28, 4.87)] were significantly associated with acute malnutrition. Conclusion: A significant number of children aged 6-59 months were affected by acute malnutrition. Younger children, vitamin A supplementation, not timely initiation of complementary feeding, and children with diarrhoea were other factors associated with acute malnutrition.