Vaccination coverage is low in Congo (10%, classified as category 4. The aim was to study the factors associated with low vaccination coverage of children aged 0-18 months in the Nkayi health district in 2023. We conducted a cross-sectional analytical study of children aged 0-18 months attending vaccination services in Nkayi. It was carried out from September 25 to October 24, 2023, and included information on socio-demographic profile, knowledge of vaccination, children's vaccination status and reasons for non-vaccination. A total of 469 mothers participated in the study. Frequencies and proportions for qualitative and quantitative variables were calculated. The average age of the mothers was 26, 67.4% were living with a partner and 56.5% had a secondary education; 96.6% of the mothers had a good knowledge of vaccination and 35% of the children were not or insufficiently vaccinated.