Due to their beneficial properties, fermented foods are considered important constituents of the human diet. They also contain bioactive peptides, health-promoting compounds studied for a wide range of effects. In this work, several antioxidant peptides extracted from fermented milk proteins were investigated. First, enriched peptide fractions were purified and analysed for their antioxidant capacity in vitro and in a cellular model. Subsequently, from the most active fractions, 23 peptides were identified by mass spectrometry MS/MS), synthesized and tested. Peptides N-15-M, E-11-F, Q-14-R and A-17-E were selected for their antioxidant effects on Caco-2 cells both in the protection against oxidative stress and inhibition of ROS production. To define their action mechanism, the activation of the Kelch-like ECH-associated protein 1/nuclear factor erythroid 2-related factor 2(Keap1/Nrf2) pathway was studied evaluating the translocation of Nrf2 from cytosol to nucleus. In cells treated with N-15-M, Q-14-R and A-17-E, a higher amount of Nrf2 was found in the nucleus with respect to the control. In addition, the three active peptides, through the activation of Keap1/Nrf2 pathway, led to overexpression and increased activity of antioxidant enzymes. Molecular docking analysis confirmed the potential ability of N-15-M, Q-14-R and A-17-E to bind Keap1, showing their destabilizing effect on Keap1/Nrf2 interaction.