Calcium carbonate (vaterite)-containing poly(lactic acid) (PLA) composites (CCPCs) were prepared for novel biomaterials that are expected to exhibit high bioresorbability and osteoconductivity. CCPC containing 30% vaterite showed bending strengths of 40~50 MPa. 13C CP/MAS-NMR spectrum of CCPC suggested the formation of a bond between Ca2+ ion and COOgroup. The bond may play an important role in the improvement of the mechanical properties. On the surface of CCPC containing 30 % vaterite, ~10-μm-thick hydroxycarbonate apatite (HCA) formed after 1 day of soaking in SBF at 37oC. After 1-week incubation of human osteoblasts (HOBs) on the HCA-coated CCPC, numerous HOBs attached. The adhesion of cells on the composite was greater than that on PLA. After 3-week culture of HOBs on HA-coated CCPC, numerous bone nodules could be seen on the surface. CCPC is believed to be one of the most promising materials for bone repair. A novel CCPC containing polysiloxane was also prepared using aminopropyltriethoxysilane (APTES). Polysiloxane partially assembled in the membrane and a molecular chain of PLA was bonded at the end of an organic chain in APTES through the amide bond formed between carboxy groups in PLA and amino groups in APTES. The composite formed HA on its surface after 3 days of soaking in SBF. The HA layer included Si with Ca and P. The composite coated with silicon-containing HCA had higher cell-proliferation ability than that without HA. The existence of silicon-containing HCA may be apt to stimulate the proliferation.