Vitamin D, a fat-soluble secosteroid, plays a key role in several metabolic diseases like diabetes. Diabetes is becoming a third leading chronic disease in the world, which seriously threatens human health. In the current study, we found the beneficial effects of vitamin D supplementation in obesity-related diabetes rat. Enzyme-linked immunosorbent assay, biochemical testing, real-time PCR and western blot were carried to investigate the effect of vitamin D supplementation on diabetes. Successful modeling of obesity-related diabetes was determined by significant weight loss and elevated levels of fasting blood glucose, glycated hemoglobin and blood lipids at 12 weeks. Supplementation of vitamin D obviously increased body weight and decreased fasting blood glucose, glycated hemoglobin, and blood lipids, accompanied by increased 25-hydroxyvitamin D and decreased insulin, parathormone and adipocytokines. Furthermore, low expressed insulin receptor substrate-1 (IRS-1)/phosphorylation of IRS-1 (p-IRS-1), glucose transporter type 4 (GluT4) and vitamin D receptor (VDR) was increased. These suggested the beneficial effects of vitamin D supplementation in obesity-related diabetes rat, which may through VDR, IRS-1/p-IRS-1, and GluT4 signaling activation.