Purpose: To compare the osseointegration at the portion of the implant within the elevated space after sinus elevation using different sizes of xenograft. Materials and Methods: Eighteen New Zealand rabbits were selected, antrostomies were prepared bilaterally through the nasal dorsum, and the sinus mucosa was elevated. Deproteinized bovine bone mineral with granules of either 1 to 2 mm (large sites) or 0.250 to 1.0 mm (small sites) were randomly used to fill the elevated space of the two sinuses. Subsequently, mini-implants were placed through the antrostomy, one in each sinus. The animals were euthanized 2, 4, and 8 weeks after surgery, six animals for each group. Microcomputed tomography (micro-CT) and histologic analyses were performed. Results: In the elevated space, at the histologic analysis after 2 weeks of healing, new bone formed on the implant surface was found in fractions of 18.8% ± 6.8% and 15.8% ± 9.6% in the large and small sites, respectively (P = .249). After 4 weeks, the respective fractions of new bone were 20.3% ± 3.5% and 23.3% ± 5.6% (P = .249). After 8 weeks, the proportions reached 33.9% ± 9.5% and 28.5% ± 10.3% (P = .173), respectively. At the micro-CT analysis, bone-to-implant contact percentage (BIC%) was 21.0% ± 2.3% and 21.2% ± 2.4% in the large and small sites, respectively (P = 1.000). The respective proportions of BIC% at the large and small sites were 20.5% ± 3.3% and 23.4% ± 5.4% after 4 weeks (P = .463), and 23.0% ± 2.7% and 25.8% ± 4.1% after 8 weeks (P = .249). Conclusion: The use of xenograft granules of different dimensions resulted in similar amounts of bone-to-implant contact at implants placed simultaneously with sinus floor augmentation. Keywords: biomaterials, bone graft, histology