A 13-year-old, 4.2 kg female poodle was referred for failure of first bilateral mandibular surgery at a local animal hospital after pathologic fracture. Surgery was performed with 2.0-mm miniplates/screws and porcine cancellous bone grafts. In addition, because of the large size of the right segmental defect, a barrier absorbable membrane was employed for guide bone regeneration on right mandible. After surgery, follow-ups performed at 1 day, 1, 4, 8, and 12 weeks; there were no signs of dental malocclusion, nonunion or soft tissue infection. However, a 1-year longterm follow-up showed nonunion in the left mandibular fracture site for which a collagen membrane had not been used. It is considered that use of porcine bone graft with barrier absorbable membrane may be effective for the repair of mandibular nonunion in a geriatric dog.