Distraction osteogenesis has had a profound impact on reconstructive mandibular surgery. To date, there has not been adequate information on the effect of distraction on the mandibular ramus to length the mandible vertically. In this study, we investigate the possibility of vertical mandibular lengthening via distraction of the mandibular ramus. Eight adult male beagle dogs underwent surgery bilaterally to place internal mandibular distraction devices via an external incision. After the distraction was performed, and the consolidation period ended, the animals were sacrificed and the newly formed bone was examined. Histological analysis along with three dimentional CT scan and fracture force measurement were all used to determaine the quality and stability of the newly formed bone. Our preliminary results identify that mandibular ramus distraction can be performed in a reliable fashion, and the quality of the newly formed bone, though more fragile than the native bone, looks as though it will stand the forces of mandibular action.