Breastfeeding is associated with reduced child morbidity and mortality, and reduced risk of breast and ovarian cancer among nursing women. Optimal breastfeeding practices are estimated to prevent almost 600,000 child deaths annually from pneumonia and diarrhea alone. However, many factors can influence breastfeeding, being the aggressive market of formula one of the most relevant. This rationale led us to investigate socioeconomic inequalities in the consumption of different types of milk by children under 2 years of age in LMICs. We used absolute and relative wealth indicators to describe socioeconomic inequalities in the consumption of breast milk (at 1 and 2 years), formula, and other types of non-human milk (under 6 months and between 6-23 months, each). Data from nationally-representative surveys conducted in 86 LMICs were used in this analysis. Consumption of breast milk was more common in poorer families in low and lower middle-income countries, than in upper middle-income countries. The latest group of countries showed the highest prevalence of formula consumption, as well as in wealthier families in all LMICs. An inverse relationship was seen between breastfeeding indicators and absolute wealth, while the reverse was reported for formula consumption in all age ranges. Associations for other non-human milk were less straightforward. Multilevel analysis showed that unmeasured factors at country level explained a substantial proportion of overall variability in formula consumption and breastfeeding. Country-level factors play an important role in explaining formula consumption by all family wealth groups, suggesting that formula marketing at national level might be partly responsible for the observed differences. A full version of the paper is available at: https://doi.org/10.1017/S1368980020004061