New abstracy Mitochondria play a central role in cellular homeostasis, energy production, and redox balance, yet the molecular mechanisms governing their response to oxidative stress remain incompletely understood. Here, we identify Protein Y as a key regulator of oxidative stress resistance and mitochondrial function in mouse embryonic fibroblasts (MEFs). Using RNA interference, we demonstrate that Protein Y knockdown leads to a significant increase in reactive oxygen species (ROS) production, as measured by DCF-DA fluorescence assays, suggesting a role in antioxidant defense. Additionally, mitochondrial membrane potential (ΔΨm) was significantly reduced upon Protein Y depletion, as assessed by JC-1 staining, indicating impaired mitochondrial integrity.Furthermore, we show that Protein Y depletion results in a 35% reduction in cell viability under oxidative stress conditions induced by hydrogen peroxide (H₂O₂) treatment. Western blot analysis confirmed efficient knockdown of Protein Y, with an 85% reduction in expression. Mechanistically, our data suggest that Protein Y regulates mitochondrial function by modulating ROS homeostasis, thereby preventing oxidative damage and preserving cellular viability.These findings provide novel insights into the role of Protein Y in mitochondrial physiology and stress adaptation, with potential implications for understanding oxidative stress-related pathologies. Future studies should investigate whether Protein Y interacts with known mitochondrial stress response pathways and whether its dysregulation contributes to disease states characterized by mitochondrial dysfunction.