Two different fabrication processes of collagen/hydroxyapatite (Col/HAp) hybrid structures were compared to investigate the inorganic/organic systems of (i) HAp nanocrystals combined with Col molecules (Col-M/HAp) and (ii) Col fibrils hybridized with the HAp nanocrystals (Col-F/HAp). The Col-M/HAp and Col-F/HAp were synthetized through the chemical reactions of the Col molecular or fibril states with HAp, indicating that the HAp crystal growth was effectively enhanced by the Col. It was found that the hybrid structures (i.e., aggregated and/or intermolecular dityrosine cross-linked states) of the Col-F/HAp with the higher density would be close to those of the fish scale. In the Col-F/HAp, the Col molecules firstly formed the fibrils to interact with the HAp nanocrystals at the hole zone. (C) 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.