True bone ceramic (TBC), obtained by twice sintering fresh bovine cancellous bone at high temperatures, is an osteoconductive and bioactive bone substitute material that exhibits excellent biocompatibility with hard tissue. The authors have previously synthesized a novel BMP-2-related peptide, P24, and found that it could enhance the osteoblastic differentiation of cells. The objective of the present study was to construct a double-modified TBC via mineralization into simulated body fluid and P24 incorporation for enhanced bone formation. In vitro experiments revealed that surface mineralization-modified (SMM) TBC scaffolds demonstrated efficiency for sustained release of P24. The P24/SMM-TBC composite exhibited increased osteogenic activity by cell adhesion rate determination, MTT assay, alkaline phosphatase staining, and calcium nodule staining with alizarin red compared with SMM-TBC and TBC. In vivo studies showed that the P24/SMM-TBC composite scaffold promoted significant bone defect repair, in marked contrast to stand-alone SMM-TBC and TBC, based on the results of radiographic evaluation and histological examination. These findings indicate that SMM-TBC is a good scaffold for the controlled release of P24 and that the P24/SMM-TBC composite could improve the adhesion, proliferation and differentiation of cells and repair bone defects. The double-modified P24/SMM-TBC composite biomaterial shows potential for clinical application in bone tissue engineering.