Transparent monolithics of poly(tetramethylene oxide) (PTMO)-modified CaO-TiO2 hybrids were obtained by hydrolysis and polycondensation of triethoxysilane end-capped poly(tetramethylene oxide) (Si-PTMO), tetraisopropyltitanate (TiPT) and calcium nitrate. Under the constant ratio of (Si-PTMO) / (TiPT) = 2/3 in mass, the molar ratio of (Ca(NO3) 2) / (TiPT) was varied from 0 to 0.15. The hybrid samples were subjected to the evaluation of the apatite-forming ability in a simulated body fluid (SBF) and to the mechanical property measurements in air by three-point bending. The apatite-forming ability in SBF remarkably increased with increasing CaO content. The hybrid samples with (Ca(NO3) 2)/(TiPT) =0.10 and 0.15 in mol formed an apatite on their surfaces within only one day. Although the Young's modulus and bending strength decreased with increasing CaO content, all the values were within the range of those of human cancellous bone. The failure strains were found to be in the range of about 13 to 25%. Thus, the hybrids exhibiting both high apatite-forming ability and high capability for deformation were successfully synthesized. These hybrids may be useful as new kind of bioactive bone-repairing materials.