Purpose: This study aimed to evaluate the effect of biphasic calcium phosphate (BCP) with high hydroxyapatite/tricalcium phosphate (HA/TCP) ratios on bone formation in rabbit calvarial defects. Materials and Methods: Sixteen New Zealand white rabbits were randomly divided into two groups, a control group and an experimental group. In each animal, bilateral circular defects (10-mm diameter) were created on the calvarium. In the control group (three rabbits per time frame), defects were grafted with autogenous bone chips in one side and left empty in the other side. In the experimental group (five rabbits per time frame), defects were grafted with BCP1 (HA:TCP, 8:2) in one side and BCP2 (HA:TCP, 9:1) in the contralateral side. The animals were sacrificed at 2 and 8 weeks as designated. Bone formation and residual grafting material were assessed by radiographic densitometry, microcomputed tomography (micro-CT), and histomorphometric analysis. Results: Histologic observation revealed that BCP1, BCP2, and the autogenous bone group preserved good contours of the defect, while the unfilled defect group showed connective tissue healing. Micro-CT analysis at 8 weeks showed the comparable percentages of bone volume fraction (% BV/TV) of BCP1 (20.70% ± 2.76%) and BCP2 (20.72% ± 3.97%) and two times higher than that of 2 weeks (9.90% ± 0.75%, 10.57% ± 0.85%). The autogenous group had a significantly (P .005) greater % BV/TV (34.58% ± 8.85%) than other groups. The percentage of the material volume fraction of BCP1 and BCP2 was not different. The histomorphometry demonstrated a higher increase in newly formed bone from 2 to 8 weeks in all groups, and all were comparable (autogenous: 4.30% ± 0.76%, 12.83% ± 7.74%; unfilled: 2.82% ± 1.19%, 8.14% ± 6.35%; BCP1: 3.01% ± 2.57%, 8.81% ± 3.86%; BCP2: 3.24% ± 1.09%, 10.27% ± 3.98%). Conclusion: BCP with a high ratio of HA presented good osteoconductive properties and space-maintaining capacity and would be beneficial for long-term preservation or when stable graft volume is essential. Schlagwörter: biphasic calcium phosphate, histomorphometry, micro-CT, nanohydroxyapatite, rabbit