Diabetes mellitus, as a major health problem for the elderly, is associated with an extensive list of complications involving nearly every tissue in the body and has been shown to alter the properties of bone and impair fracture healing in both human and animals. The objective of this study was to examine the healing process of a mandibular fracture in the streptozotocin-induced rats histomorphometrically and histologically. A standardized fracture model was chosen and based on blood-glucose value at the time of surgery. A total of 11-weeks old 36 rats were divided into 2 groups; One is a streptozotocin-induced diabetic group and the other is a non-diabetic group. All was fractured experimentally. Three animals from each group were killed 1, 2, 4, 6, 8 and 12 weeks after fracture and specimens were processed undecalcified for quantitative bone histomorphometric and histologic studies. The diabetic group showed a significant decrease of histomorphometry-based parameter including trabecular bone volume, trabecular thickness in comparison to the non-diabetic rat. This was confirmed histologically. In conclusion, this study suggests that in streptozotocin-induced diabetics, the healing process of bone fracture was impaired and delayed about 2-3 weeks comparing to non-diabetics.