Scaffold of hydroxyapatite for further tissue-engineering application was produced by hydrothermal treatment of cuttlefish bone originated aragonite at 200°C. Aragonite (CaCO3) monoliths were completely transformed into hydroxyapatite after 48 hours of HT treatment. The substitution of CO3- groups predominantly into the PO4 3- sites of the Ca10(PO4)6(OH)2 structure was suggested by FTIR spectroscopy. SEM micrographs have shown that the interconnected hollow structure with pillars connecting parallel lamellae in cuttlefish bone is maintained after conversion. Specific surface area (SBET) and total pore volume increased and mean pore size decreased by HT treatment.