Diabetes mellitus (DM) is a kind of metabolic disorder characterized by long-term hyperglycemia. Oxidative stress is involved in inducing the apoptosis of pancreatic β-cells and promoting the development of DM. Oxalomalate (OMA) is a competitive inhibitor of two classes of NADP+-dependent isocitrate dehydrogenase isoenzymes that are the main nicotinamide adenine dinucleotide phosphate (NADPH) producers to scavenge cellular reactive oxygen species (ROS). However, the role of OMA in DM remains unclear. The present study aimed to investigate the protective effects of OMA on streptozotocin (STZ)-induced β-cell damage and its underlying mechanisms. The viability of rat insulinoma cell line (INS-1) and the contents of ROS, nitric oxide and NAPDH were examined after cells being treated with STZ. After treatment with OMA in STZ-stimulated INS-1, the cell viability, apoptosis, and apoptosis-related proteins were measured. Meanwhile, the levels of oxidative stress-related factors and the changes of insulin secretion were determined. The results revealed that OMA significantly increased the cell viability (p < .05), reduced the apoptotic rate (p < .001), and altered the expression levels of Bcl-2, Bax, cleaved caspase3, and cleaved-caspase9 (p < .05 or p < .01) in STZ-induced INS-1 cells. Moreover, OMA enhanced the activities of superoxide dismutase, catalase, glutathione peroxidase (p < .01), whereas reduced the levels of ROS, malondialdehyde and lactic dehydrogenase (p < .001). Furthermore, OMA improved the ability of insulin secretion. These results indicated that OMA might have antioxidative stress and anti-apoptosis effects to protect INS-1 cells from STZ-induced cell damage.