S. aureus mastitis is prone to recurrence partly because of S. aureus ability to invade bovine Mammary Epithelial Cell (bMEC). One sustainable way to treat or prevent mastitis is the use of Lactic Acid Bacteria (LAB), naturally present in the teat ecosystem, as mammary probiotics. In this study, we tested the inhibitory potential of L. casei strains against invasion of bMEC by two S. aureus strains, RF122 and NB305, which generate acute and moderate mastitis, respectively. Our results indicated that adhesion and internalization capacities were higher for NB305 than for RF122. In addition, L. casei strains impaired, in a contact-dependent way, adhesion and internalization of S. aureus without altering viability of bMEC. This first study on the antagonism of LAB against S. aureus in a mammary context opens new avenues for the development of prevention strategies against this pathogen.