OBJECTIVE To investigate the preventive effect of low-intensity ultrasound on osteoradionecrosis of jaws (ORNJ). METHODS Twenty-five canines were randomly divided into experimental group (n=20) and control group (n=5). The canines in experimental group received radiation exposure, and then were randomly subdivided into group A (n=10) and group B (n=10). Control group did not undergo radiotherapy. One month after radiotherapy, the fourth mandibular premolars of all animals were extracted. Group B was immediately treated by low-intensity ultrasound for twenty days, group A and control group did not receive any treatment. Two months after tooth extraction, the formation of ORNJ was determined and the occurrence rate of ORNJ was compared between group A and B. The microstructure of the mandible and changes in microvascular density in group A and B were evaluated and compared with those of control group. RESULTS All animals in group B and group A developed ORNJ after prophylactic ultrasound was applied for twenty days. Although the imaging examination of bony density of group A and B were lower than normal animals in control group, bone density in group B was significantly better than group A. Micro-CT showed that the trabecular bone volume fraction, trabecular thickness, bone surface/bone volume and trabecular number in group B were respectively (0.187±0.029)%, (0.160±0.039) µm, (12.536±2.558)/mm, (1.227±0.192)/mm, which were all greater than group A [(0.103±0.014)%, (0.069±0.013) µm, (5.598±0.731)/mm, (0.522±0.064)/mm)] (P<0.05). CONCLUSIONS Although the preventive application of low intensity ultrasound can not prevent the formation of ORNJ, but can significantly improve the symptoms of ORNJ.