Introducing commercial milk formula (CMF) as prelacteal feeds can disturb exclusive breastfeeding and shorten breastfeeding duration. However, the prelacteal feeding of CMF has been growing alongside its increasing sales in Indonesia. This study examined predictors of the CMF feeding in the Malang and Sidoarjo districts of Indonesia. This analysis used post‐delivery data collected from 676 mothers in a cohort evaluation of a cluster randomised controlled trial (Baduta study). Multivariate random effects logistic models were employed to assess factors associated with the CMF feeding. A total of 467 (69.1%) respondents reported giving CMF to their infants during the first 3 days after delivery. Mothers with low breastfeeding self‐efficacy (BFSE) were at a higher risk of providing CMF within 3 days of birth compared to those with medium or high BFSE (adjusted odds ratio (aOR) 8.12; 95% confidence interval (CI) (4.26–15.48). Receiving explanations to solve breastfeeding problems from health professionals (aOR: 1.87; 97% CI: 1.12–3.11) and primipara parity (aOR: 1.71; 95% CI: 1.12–3.04) were positively associated with the CMF feeding. Early initiation of breastfeeding (EIBF) was protective against CMF feeding (aOR: 0.40; 95% CI: 0.22–0.58). There was an interaction between EIBF and BFSE. EIBF was protective among mothers with high or medium BFSE, but had no effect among those with low BFSE. CMF feeding was prevalent in Indonesia. Future strategies should focus on improving health‐staff capacity to strengthen BFSE during pregnancy and provide adequate counselling for mothers with breastfeeding problems.. Prelacteal feeding of commercial milk formula was prevalent in Indonesia. Future strategies should focus on improving health‐staff capacity to strengthen breastfeeding self‐efficacy during pregnancy and provide adequate counselling for mothers with breastfeeding problems as both factors are the important determinants of this harmful practice. .