The purpose of this study was to evaluate the effect of chitosan-calcium sulfate mixture on early bony consolidation in osteodistracted dogs. The experimental group was divided into 3 groups: saline group(Control), chitosan group(Group CH) and chitosan-calcium sulfate mixture group(Group CH+CS). Four dogs were allocated to each group and classified into B week observation subgroups and 5 week observation subgroups, respectively. Two dogs were allocated to each subgroup. The lateral surface of the left mandibular body was exposed in the subperiosteal plane and vertical osteotomy was carried out on the mandibular body. An external distraction device was applied to the mandibular body. Mandibular distraction was started 5 days after the osteotomy at a rate of 1 m per day for a total of 10 w distraction for 10 days. After completion of distraction, chitosan, chitosan-calcium sulfate and saline were injected into the distracted zone of the group CH, group CH+CS and control. The external device was left in place for 3 or 5 weeks to allow for bony consolidation. Serial radiographs were carried out every week. Two dogs of each group, six dogs in total, were sacrificed at 3 weeks, and the other six dogs at 5 week after distraction. Bone specimens of the distracted mandibles were taken for histologic examination. New bone was not noted in the distracted zone of 3 week observation subgroups in the control and group CH. However, new bone was developed in the group CH+CS with a narrow fibrous interzone in the area of the distracted zone. While osteogenesis was mild in the margin of the distracted Bone of 5 week observation subgroup in the control, new bone was noted much in the group CH and group CH+CS. However, osteogenesis was noted more significantly in the group CH+CS than that of group CH. In conclusion, chitosan-calcium sulfate mixture was more effective on early bony consolidation in distraction osteogenesis