Purpose: This study compared the volume stability and bone-forming capacity of biphasic calcium phosphate (BCP) with a high versus a low ratio of β-tricalcium phosphate (β-TCP) relative to hydroxyapatite (HA), ie, 70:30 vs 30:70, in the rabbit sinus model. Materials and Methods: Bilateral sinus windows were created in eight adult New Zealand white rabbits (2.5 to 3.5 kg); each sinus in each rabbit was assigned to one of two experimental BCP groups according to the HA:β-TCP ratio. One sinus was grafted with BCP with a high ratio of β-TCP (30:70; TCP70), and the contralateral sinus was grafted with BCP with a low ratio of β-TCP (70:30; TCP30). The animals were sacrificed after 2 weeks (n = 4) or 8 weeks (n = 4) of healing. Biopsy specimens were harvested and evaluated histologically, histomorphometrically, and with microcomputed tomography. Results: The bone volume did not differ significantly between the two groups at each healing point, or between 2 and 8 weeks of healing in both groups. The amount of new bone increased significantly between 2 and 8 weeks of healing in both groups, and it did not differ significantly between the TCP30 and TCP70 groups. The residual material was significantly more resorbed in the TCP70 group than in the TCP30 group at both 2 and 8 weeks. In the TCP70 group, a greater number of multinucleated giant cells were observed at both weeks. The bone-to-residual material contact ratio did not differ significantly between the two groups. Conclusion: The volume stability and osteoconductive capacity of BCP with an HA:β-TCP ratio of 30:70 was comparable to that with an HA:β-TCP ratio of 70:30. Thus, within the limitations of this study, it can be argued that BCP with an HA:β-TCP ratio of 30:70 can be successfully used for sinus augmentation. Keywords: biphasic calcium phosphate, bone regeneration, rabbit sinus model, sinus augmentation