We have identified the effects of oligonol, a low-molecular polyphenol derived from lychee fruit, on diabetes-induced pancreatic damage via oxidative stress. Oligonol was orally administered at 10 or 20 mg (kg d)(-1) for 10 days to streptozotocin (STZ)-induced diabetic rats, and we assessed the changes in the serum glucose and insulin levels, as well as those of body weight and food and water consumption. In addition, analyses of the weight, insulin content, reactive oxygen species (ROS) level, and western blots of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-4 (Nox-4), p22(phox), p47(phox), phosphor-c-Jun N-terminal kinase (p-JNK), Bax, cytochrome c, caspase 3, pancreatic-duodenal homeobox (PDX-1) and cyclin E were also performed in the pancreas. However, these unfavorable outcomes under diabetes were reversed by oligonol administration. Oligonol treatment led to significantly attenuated histological damage in the pancreas. In conclusion, this study suggests that oligonol protects the pancreas from Bax and PDX-1 via oxidative stress for the prevention or delaying of diabetes mellitus.