Purpose: The effect of hydroxyapatite (HA) crystallinity on protein adsorption and osteoblast precursor cell attachment to HA was investigated. Materials and Methods: Different weight ratios of 100% crystalline HA and 100% amorphous calcium phosphate powders were mixed and pressed into disks (0.5 g) of different crystallinities-either 0% (HA0), 30% (HA30), 50% (HA50), 70% (HA70), or 100% (HA100). Results: X-ray diffraction indicated differences in HA crystallinities. In addition, dissolution of the HA was dependent on its crystallinity, with an increase in phosphorus dissolution as the degree of crystallinity was decreased. No significant difference in albumin adsorption and initial osteoblast precursor cell attachment was observed in the range of HA0 to HA70 surfaces. However, a significantly lower albumin adsorption and initial osteoblast precursor cell attachment were observed on HA100. Discussion: It was suggested that changes in ionic interactions as a result of a change in crystallinity affect the amount of calcium ion ligands readily available to electrostatically bind to proteins. Conclusion: It was thus concluded from this study that HA crystallinity affects the amount of albumin adsorbed and initial osteoblast attachment.