Natural bone has excellent mechanical properties such as high fracture toughness and high flexibility. These properties are achieved by specific microstructure of natural bone that is composed of the organic collagen and inorganic apatite. On the basis of these findings, apatite-polymer hybrids are expected as novel bone substitutes having excellent mehcanical performances and high bone-bonding ability, i.e. bioactivity. In this study, we attempted preparation of apatite-polyglutamic acid hybrids through biomimetic process that mimics the principle of biomineralization. Simple chemical modification of the polyglutamic acid gel with 1 M (= mol/L) calcium chloride solution provided the gel with apatite-forming ability in simulated body fluid (SBF, Kokubo solution). This type of hybrid is also useful for designing bioactive bone substitutes with injectability, since viscosity of the polyglutamic acid gel can be easily controlled according to degree of cross-linking.