The World Health Organization recommends deworming to reduce soil-transmitted helminth (STH)-attributable morbidity in women of reproductive age, including pregnant and lactating women, to reduce blood loss, iron deficiency anaemia and nutrient malabsorption. This study assessed the impact of maternal postpartum deworming with albendazole approximately 1 day after delivery on infant milk intake among a subset of 216 randomly selected mother–infant pairs recruited into a large trial in Peru. Infant milk intake was measured using the deuterium-oxide method at 1- and 6-month postpartum. Maternal STH infection was measured at 6-month postpartum. At 1-month postpartum, mean intake was 756 ± 16 and 774 ± 18 mL day−1 in the albendazole and placebo groups, respectively (mean difference: −18 mL day−1; 95% CI: −65, 30). At 6-month postpartum, mean intake was 903 ± 16 and 908 ± 18 mL day−1 in the albendazole and placebo groups, respectively (mean difference: −5 mL day−1; 95% CI: −52, 43). There was no statistically significant difference in milk intake between groups at either time point. At 6-month postpartum, mothers infected with Trichuris trichiura had infants with higher milk intakes (adjusted mean difference: 70 mL day−1; 95% CI: 20, 120) compared with uninfected mothers. However, there was no statistically significant difference in infant milk intake between mothers who had moderate-and-heavy intensity infection compared with the comparison group (mothers with no and light intensity infection). A lower prevalence and intensity of infection, and inclusion of uninfected mothers in both arms of the trial, resulting in effect dilution, may explain the null findings.