The protein adsorption behavior onto sheet-like calcium hydroxyapatite Can(PO4)(6)(OH)(2) (Hap) particles produced by microreactor was examined by using typical acidic bovine serum albumin (BSA) and basic lysozyme (LSZ). Since the sheet-like Hap particles were highly growth through b- (or a-) and c-axes, the particles had larger fraction of bc (or ac) crystal face. The saturated amounts of adsorbed BSA (n(s)(BSA)) for the sheet-like Hap nanoparticles were increased with increase in the particle size; i.e., n(s)(BSA) showed a good linear relationship with the total surface area of bc and ac faces of each particle. This result strongly suggested that the sheet-like Hap particles progressed in b- and c-axes with large fraction of C sites on bc and ac particle faces and exhibit a high selective adsorption of BSA. On the contrary, very few LSZ molecules adsorbed onto sheet-like Hap particles. Hence the present study developed that the amounts of adsorbed protein, especially for BSA, can be controlled optimally by altering the size of sheet-like Hap particles. It was also found that the sheet-like Hap particles can be applied to separate completely BSA molecules from BSA-LSZ mixed solution. (C) 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.