There is emerging evidence that the generation of reactive oxygen species (ROS), which leads to dysfunction of pancreatic beta-cells, is a major factor in the development of type 2 diabetes mellitus. Antioxidation is one of the therapeutic strategies to overwhelm the imbalance in ROS production. In this study, a herbal formulation SR10, comprising Radix Astragali, Radix Codonopsis and Cortex Lycii, was examined for its antidiabetic and antioxidative effects using the diabetic +db/+db mouse model. The results showed that SR10 was effective in decreasing the blood glucose level in chronic treatment by improving beta-cell function. The activities and expression of antioxidant enzymes, catalase and superoxide dismutase, were up-regulated when treated with SR10. Moreover, SR10 treatment did not exhibit any toxic effect to the host.