Introduction: Acute malnutrition is defined by the weight / height (W/ H) index <- 2 Z-score at the median of the WHO standards. It is responsible for 45% of deaths of children under 5 in developing countries. Objectives: To determine the prevalence and determinants of malnutrition among children under five in the district of Djiri in Brazzaville in 2018. Methods: An analytical cross-sectional study was conducted on 482 mother-child pairs whose children were aged 6-59 months in the Djiri district of Brazzaville. We collected data from May 30 to July 15, 2018. We identified the factors associated with acute malnutrition. Anthro 2005 and Epi-info version 7.2. softwares were used for storage and analysis of data. The influence of the variables on the occurrence of acute malnutrition was calculated using Chi2, Odds Ratio with 95% CI. The level of significance was set up at p <0.05. Results: The prevalence of acute malnutrition or wasting was (40/482) 8.3%. Factors associated with acute malnutrition were age less than 23 months [ORa: 2.10 (1.30- 3,37); p = 0.0016], birth weightless than2500g, [ORa: 3.23 (1.82-5.72); p = 0.001] and households with more than 7 persons [ORa: 2.28 (1.31-3.96), p = 0.01]. Conclusion: Preventive measures are needed to reduce their prevalence.