The present study was designed to investigate whether an octacalcium phosphate/gelatin (OCP/Gel) composite can repair a defect created in rabbit tibia within 4 and 6 weeks. Histological and μCT studies showed that the implantation of OCP/Gel composite enhanced cortical bone formation over the defect accompanied by the formation of cancellous bone within 6 weeks. The defects were not almost repaired in the control group (gelatin only) within 4 weeks. The repaired cortical bone by gelatin was thinner than that in the OCP/Gel-implanted group. The results suggest that an OCP/Gel composite could be effectively used as a bone substitute material.