To explore some new approaches to designing novel mimetic architecture for bone implant materials, the conversion of a natural ceramic of Saxidomus purpuratus shell to hydroxyapatite (HAp) was investigated in the present study by using a pre-treatment in phosphate buffer solution (PBS) and an in vitro assessment in stimulated body fluid (SBF) solution. The main concern was focused on a comparison of in vitro bioactivity on the outer layer (porous fibrous/blocky structure) and inner layer (complex crossed-lamellar) of the shell. It is found that the apatites are deposited more compactly on the surface of porous blocky layer than crossed-lamellar layer in the preliminary stage of immersion in PBS for the same time. However, after a subsequent in vitro mineralization in SBF for a relatively long time of 4weeks, the bioactive bone-like apatite layers are formed on the both inner and outer layers with different structures. Importantly, the results have demonstrated that the crossed lamellar structure with a good combination of mechanical and biological performances can be well referenced as a bio-inspired composite structure for hard tissue replacements.