Diseases with faeco-oral route of transmission remain a problem of public health importance, majority of which can be attributed to unsanitary handling of child faeces. This study aimed to assess the patterns and determinants of sanitary handling of child faecal matter among mothers of under-5 children in Osun State, Nigeria. A descriptive cross-sectional study design was employed to study 598 mothers in Osun State. A multistage sampling technique was adopted for the recruitment. Data were collected using an interviewer-administered questionnaire and a checklist was used to assess the sanitation of the houses. Determinants of sanitary disposal of child faeces were assessed using binary logistic regression. Sanitary handling of child faeces was practiced by 337 (56.4%) mothers. Knowledge of the harmful effects of improper child faecal handling, sanitation index, and religion were observed to be significant determinants of sanitary disposal of child faeces. Increase in the knowledge score increased probability of sanitary child faecal handling (B=0.403, 95% CI=1.088-2.060, p=0.013). Poor sanitation index had a negative relationship with the practice of sanitary child faecal handling (B=-0.180, 95% CI=0.789-0.885, p<0.001). The Muslims were 1.7 times more likely to practice sanitary disposal of child faeces than Christians (Odds ratio=0.6, 95% CI=0.352-0.872, p=0.011). A significant number of mothers still practice unsanitary handling of their children's faeces which predisposes the duo to diseases. Strengthening health promotion programmes in this regard is imperative.