This study was carried-out to evaluate the reaction of the periodontiume to orthodontic force in diabetic rats and to detect the nitric oxide with its tissue response during bone remodeling. The sample consisted of eighteen male albino rats at the beginning of the study and ended by sixteen rats due to sample decay. The sample was divided into two equal groups. The first group (8 rats) was used as non-diabetic controls. The second group (8 rats) served as the diabetic group and was treated by single intraperitoneal injection of Streptozotocin*(STZ) with 50 Mg/Kg dissolved in citrate-buffered saline solution, (ph= 4.5). The orthodontic treatment was tried in many ways; a spring (one ounce force) was stretched between the two mandibular incisors to elicit expansion. The spring was designed in such a way that a helix was constructed in a single vertical loop and attached to the teeth by eyelets(14) . Then, different sizes of elastic separators retented by kobayashi ligatures. The specimens were taken, washed, fixed in fixative solution, put in EDTA for decalcification and after that prepared until reached to paraffin embedding. Specimens stained by haematoxilin and eosin(15), Mason's trichrome(16). And then the immunohistochemical staining of NOS . The diabetic group showed greater numbers of osteoclast cells in their lacuna indicating more bone resorption compared to non diabetic rats. In spite of highly expression of the NO in the pressure side of the diabetic group, it was founded with low reaction in the tension side. Depending on the results of this study, the diabetic rats showed greater bone resorption at the pressure side and retarded bone deposition at the tension side compared to the healthy rats. Hence, orthodontist should consider these results by using a very light force, increasing the gaps between visits, planning to decrease the range of tooth movement, monitoring the oral hygiene and sharing with patients physicians for controlling diabetes during orthodontic managements.