The high mortality of children under-five is worrying. The World Summit for Children (1990) aimed to reduce by 1/3 its level from 1990 to 2000. Similarly, the Sustainable Development Goals for their part, aimed at a level of 25‰ at most by 2030. In Guinea, this mortality of children under-five remains high (108‰ in 2018). Previous studies have largely highlighted the main determinants of this mortality of children under-five, but their influence at different levels of analysis remains little known and documented. This study contributes to this by measuring the influence of individual, family and regional factors. The application of a multilevel logistic regression to data from the Demographic and Health Surveys (2018) shows that the individual factors (birth ranks, mother's level of education, ethnicity, age at childbirth), family factors (household standard of living) and regional factors (degree of ethnic heterogeneity, vaccination coverage and mothers' literacy) are significant in explaining this mortality.