Despite evidence showing that the intake of ultra-processed food has a negative impact on health, diet quality and dietary vitamin E, its impact on vitamin E nutritional status and breast milk remains unknown. This study aimed to assess the influence of the consumption of ultra-processed foods on vitamin E biomarkers of lactating women. A cross-sectional study was performed with 294 lactating women. Food consumption was obtained by 24-h dietary recall, and foods were grouped according to the NOVA classification. Levels of α-tocopherol were analysed by HPLC. Breast milk vitamin E (BMVE) adequacy was based on the quantity of the vitamin in the estimated intake volume. The Kruskal–Wallis test was used to compare the tertiles and linear regression to association between ultra-processed food consumption and biomarkers. Ultra-processed foods accounted for 16 % of energy intake and vitamin E intakes by all women were considered low. Serum α-tocopherol was 26·55 (sd 7·98) µmol/l, 5 % (n 11) showed inadequate vitamin E (< 12 µmol/l) and 78 % had an inadequate BMVE content (< 4 mg/780 ml). The regression showed that a higher dietary share of ultra-processed foods was associated with lower concentrations of serum α-tocopherol (β = –0·168, 95 % CI –0·047, 0·010, P = 0·003) and inadequate BMVE content (β = –0·144, 95 % CI = –0·505, 0·063, P = 0·012) (adjustment for income and maternal age). Thus, higher dietary shares of ultra-processed foods had an impact on vitamin E biomarkers, suggesting that inadequate dietary intake practices during lactation may reduce the supply of vitamin E to women and breast milk.