The size of inorganic particles used as adsorbents and drug carriers affects protein adsorption behavior. In this study, the protein adsorption behaviors of various inorganic milled particles, including activated bamboo charcoal (ABC), silica (SiO2), and hydroxyapatite (HAp) were investigated. Various inorganic particles were milled for different periods to reduce the particle size and enhance protein adsorption. A bicinchoninic acid test (BCA) kit was employed to assess the adsorption and desorption behaviors of bovine serum albumin (BSA) on inorganic particles. The increased amount of BSA adsorbed on the inorganic particles was correlated with the smaller sizes of the inorganic particles. Owing to the electrostatic interaction between COO- groups and Ca2+ ions on the surface of HAp, which is essential for the adsorption of acidic BSA molecules, HAp showed a higher ability to bind BSA. Furthermore, the protein released from inorganic-proteins steadily increased in a phosphate buffer solution (PBS). The amount of protein released from the HAp-protein was much lower than that from other inorganic-proteins due to the strong immobilization of the HAp-protein. According to these findings, the particle size and physicochemical properties of the adsorbents significantly affected the adsorption behavior of acidic protein adsorbates.