An increase in bone fracture risk has been reported in patients with diabetes. To evaluate an early effect of glucose intolerance on bone homeostasis, we have characterized bones from spontaneously diabetic torii (SDT) rats, an animal model of type 2 diabetes in comparison with Sprague Dawley (SD) rats as healthy control. Focusing on early effects of diabetes on bone elasticity, longitudinal wave velocities of animal bones were first determined by a micro-Brillouin scattering technique in a non-destructive way. Wave velocities in the cortical and cancellous bones in the tibias of the SDT and SD rats were compared. In a pre-diabetic stage at approximately 10 weeks of age, there seems no significant difference in wave velocities in bones from age-matched SDT and SD rats. By contrast, after the onset of diabetes at approximately 20 weeks of age, the mean velocities of bones from SDT rats were lower than those of SD rat. In addition, the X-ray CT showed that the bone amounts of SDT rats were smaller than those of SD rats in an early diabetic stage at 20 weeks of age. The current study demonstrated that the wave velocity decreased in bones of SDT rats in the early stages of diabetes. While a decrease of bone strength in an early stage of diabetes can be partially explained from decreases in bone amount as well as bone elasticity, further studies will be needed in understanding a detailed mechanism of bone deterioration due to diabetes.