The effect of platelet rich plasma (PRP) on osteogenesis in the defect of long bone is controversial. The purpose of this study was to investigate the effect of PRP on new bone formation in a segmental defect of rabbit ulna. Unilateral 15 mm mid-diaphyseal defect was created in the ulna of twenty skeletally mature New Zealand White rabbits. The defects in ten rabbits each were treated with autogenous PRP in a polycarprolactone scaffold (PRP treated group) and remain empty defect without any material (contol group). 12 weeks and 20 weeks after surgery, five rabbits in each group were sacrificed to assess new bone formation. New bone formation assessed by plain radiography, microCT scan and histology did not differ significantly between PRP treated group and control group. This study demonstrated that PRP alone had no evidence of promoting osteogenesis in a long bone segmental defect of rabbit ulna.