Purpose: The aim of this study was to compare two different forms of bovine-derived hydroxyapatite (HA) in sinus augmentation and simultaneous implant placement. Materials and Methods: The schneiderian membranes of 12 domestic pigs were elevated bilaterally through an extraoral approach. One sinus of each pig was grafted with bovine-derived granular HA (GHA) and the other was grafted with bovine-derived spongiosa block HA (BHA) (Unilab Surgibone). One dental implant was placed simultaneously into each grafted sinus. Animals were sacrificed after 6 months of healing. Primary implant stability (ISQi) and secondary implant stability (ISQf) were measured by resonance frequency analysis. Undecalcified sections were prepared for histomorphometric analysis. Results: Mean ISQi values for implants placed in sinuses grafted with BHA and GHA were 68.8 ± 5.0 and 68.2 ± 3.7, respectively (P > .05). The mean ISQf value for implants in GHA increased to 72.0 ± 5.1 and for implants in BHA decreased to 52.3 ± 8.8 (P .01). There was a statistically significant difference between ISQi and ISQf values for implants placed in BHA (P = .03) and GHA (P = .037). Mean boneimplant contact (BIC) in residual bone was 61.3% ± 2.1% for BHA and 61.2% ± 1.7% for GHA (P > .05). In augmented bone, mean BIC percentages were 20.6% ± 2.1% and 35.6% ± 1.8% for BHA and GHA, respectively (P = .002). Mean percentages of connective tissue were 61.9% ± 9.5% and 48.4% ± 10.7% (P = .036), new bone formation percentages were 12.8% ± 5.5% and 27.9% ± 4.6% (P = .012), and percentages of graft material around the implants were 25.3% ± 5.8% and 22.4% ± 6.2% (P > .05) for BHA and GHA, respectively. Conclusion: The form of graft material affects the osseointegration of implants in sinus augmentation and simultaneous implant placement. Keywords: bovine-derived hydroxyapatite, dental implants, histomorphometry, resonance frequency analysis, sinus augmentation