Abstract: Objective To investigate blone formation,material′s degradability and biological safety using selfdesigned degradable AZ31 magnesium alloy distractor on mandibular distraction osteogenesis (DO).Methods 12 mongrel dogs were used in this study.Unilateral three odontoprisis were moved out 3 months before mandibular osteotomy.Then,unilateral mandibular osteotomy was performed on 12 dogs.By operation,selfmade magnesium alloy and stainless steel distractors were implanted.After 5 days′ latency,the dogs in two groups underwent distraction at the rate of 0.3 mm/8 h for 7 days and entered into consolidation period.12 dogs were respectively sacrificed at the fourth week after consolidation.Vertical height measurements of mandibles,scanning electron microscopy (SEM),histological and liverkidney pathological evaluations were performed,but nothing abnormal was detected.Results The segments in alveolar direction were augmented (6.300±0.018) mm in experimental group and (6.307±0.027) mm in control group.There were no obvious differences (P>0.05).Active osteoblasts,trabeculae and a little mature bone tissue gradually formed in distraction space of two groups.There were obvious cracks on surfaces of the magnesium alloy.There were no abnormalities in the pathological analysis of liver and kidney tissue in experimental group.Conclusions It suggests that four weeks after distraction with AZ31 magnesium alloy distractor,the height of mandibular has been increased and an adequate bone has been created.AZ31 magnesium alloy has a certain degradation speed in mandibles.AZ31 magnesium alloy has not any negative effect on liver and kidney tissues.