Silicone elastomer was chemically treated at 60℃ for 7 days with 30 wt% H(2)O(2) solutions with or without TaCl(5) and soaked for various periods in a simulated body fluid(Kokubo solution) up to 21 days. Apatite formation ability of the surface of the silicone elastomer specimens was investigated with thin-film X-ray diffraction and FT-IR reflection spectroscopy. These silicone specimens did not deposit apatite or calcium phosphates, irrespective of chemical treatment. Osteoblast-like cells (MC3T3-El) derived from mouse were cultured on the specimens at 36.5℃ under 5%C0(2) and 95% humidity. Similar degree of proliferation of cells was observed at 7 days among three specimens, while the no treatment specimen after incubation for 5 days showed a lower degree of proliferation than the silicone treated with 30 wt% H(2)O(2) solutions with or without TaCl(5). Alkaline phosphatase activity of the cells proliferated on the no treatment specimen was lower than those of the silicone treated with 30 wt% H(2)O(2) solutions with or without TaCl(5). These results indicate that the cytotoxicity of the silicone could be improved by the chemical treatment with 30 wt% H(2)O(2) solutions with or without TaCl(5).