Breastfeeding's influence on the tolerance to environmental antigens is essential for short- and long-term homeostasis for children. Colostrum is rich in leucocytes, but it is unknown whether regulatory T cells (Treg) account for part of this cell population. Frequencies of CD127-  CD25++ Treg and levels of immunoregulatory-associated cell markers were determined in colostrum and were compared with autologous blood cells. In addition, we evaluated whether the birth conditions can affect these features. Higher frequencies of CD127 - CD25++ Treg cells expressing Foxp3 and CD45RO were observed in the colostrum. The cells' CD25, CD152, CD279, and TGF-β expression levels were greater than those in autologous blood cells. In addition, the CD279 and TGF-β expressions of colostrum CD127-  CD25++ Treg cells were influenced by gestational age and delivery mode. The higher proportion of these cells with a function-associated phenotype may reflect certain tolerogenic effects of breastmilk on newborns and infants, contributing to immune system homeostasis. © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.