Purpose: To optimize methods for seeding cells on granular-type beta-tricalcium phosphate (β-TCP). Materials and Methods: Bone marrow stromal cells were obtained from rat long bones and cultured in flasks with Minimum Essential Medium, Alpha Modification (αMEM) supplemented with 10% fetal bovine serum (FBS), dexamethasone, ascorbic acid, β-glycerophosphate, and antibiotics. The influence of differential cell seeding densities and dynamic cell seeding conditions (rotation) was investigated using different sizes of β-TCP granules and a subcutaneous implantation model. Results: Higher cell seeding densities contributed to efficient in vivo bone formation. The rotational seeding did not affect the efficiency but contributed to the uniformity. Although the granule size did not affect the efficiency under the conditions used in this study, large granules showed more uniform distribution of bone regeneration, while small granules showed nonuniform but dense bone formation. Mixtures of relatively large and small granules may be beneficial for both uniform and efficient bone regeneration. Conclusion: These findings may contribute to stable bone tissue engineering with bone marrow stromal cells and β-TCP granules as a scaffold. Keywords: bone tissue engineering, β-TCP, cell seeding, granular scaffold, in vivo bone formation