Micrometer-sized hydroxyapatite (HA) with rod-shape was prepared to investigate protein adsorption onto its crystal face, through hydrothermal processing. Adsorption of Bovine serum albumin (BSA) and Lysozyme from chicken egg white (LSZ) on rod-shaped HA crystals with approximately 50 μm in length and 1 μm thickness was examined in phosphate buffer solution. The amount of adsorbed BSA was decreased with increasing phosphate concentration in the examined solution. Adsorption of LSZ was increased with increasing phosphate concentration in the buffer solution up to 50 mmol/L (mM), while it was remarkably decreased when the phosphate concentration reached approximately 100 mM. These phenomena lead to understanding of chromatographic characters of HA for separation of acidic and basic proteins.