Among the many environmental stresses, excessive production of reactive oxygen species (ROS) and the ensuring oxidative stress are known to cause significant cellular damage. This has clinical implications in the onset of type 1 diabetes, which is triggered by the destruction of pancreatic β-cells and is associated with oxidative stress. In this study, we investigated the protective and antioxidative effects of mulberry extract (ME) in insulin-producing pancreatic β-cells. We found that ME protects pancreatic β-cells against hydrogen peroxide (H2O2)-induced oxidative stress and the associated apoptotic cell death. ME treatment significantly reduced the levels of H2O2-induced 2-diphenyl-1-picrylhydrazyl (DPPH) radicals, and lipid peroxidation and intracellular ROS accumulation. In addition, ME inhibited DNA condensation and/or fragmentation induced by H2O2. These results suggest that ME protects pancreatic β-cells against hydrogen peroxide-induced oxidative stress.