Purpose: The purpose of this study was to investigate the impact of graft bone particle size on autogenous bone graft augmentation in a vertical augmentation chamber model. Materials and Methods: A total of 12 rabbits were used in this study. The donor bone particles were of different sizes: small (150 to 400 μm), large (1.0 to 2.0 mm), and a mixture comprising equal weights of both large and small bone particles. One type of bone graft material was placed into each of two polytetrafluoroethylene chambers that were implanted in the parietal bone of each rabbit's cranium. Animals were sacrificed 4 or 8 weeks after the grafting procedure. The recovered samples were analyzed by microcomputed tomography (micro-CT) for quantitative analysis. Total bone volume, bone height, and the distribution of bone structure were calculated by micro-CT. Results: Micro-CT evaluations revealed that the bone grafts performed with large bone particles provided, statistically, the best outcome. Total bone volume and bone height decreased in a time-dependent manner, and there was a statistically significant reduction in total bone volume between 4 and 8 weeks in the group with the mixed bone particle sizes. Conclusion: Within the limitations of the present study, large bone graft particles provided the best preservation of total bone volume and bone height up to 8 weeks after grafting in an animal vertical augmentation model. Keywords: animal study, autogenous bone particle size, micro-CT, vertical augmentation graft