Apatite-polymer hybrid has attractive features as novel bone substitutes such as both ability of bone-bonding and mechanical performances analogous to those of natural bone, i.e. high strength and high flexibility. As a method for development of such hybrids, biomimetic process has been proposed, where apatite formation is induced on the surfaces of organic substrates at ambient conditions in simulated body fluid (SBF) with ion concentrations similar to those of human extracellular fluid, or related solutions supersaturated with respect to the apatite. In this process, heterogeneous nucleation of apatite is triggered by specific functional groups. This apatite nucleation is enhanced by release of calcium ions (Ca2+) from the materials which increases degree of supersaturation of surrounding fluid with respect to apatite. In the present study, we attempted to prepare apatite-polyamide hybrids by biomimetic process. Polysaccharides and natural polypeptides containing carboxyl group (-COOH) were used as a starting material, and apatite formation ability was compared. It was found that the apatite formation was governed by not only content of the carboxyl group but also ionic interaction with Ca2+.