Ti, a Ni-Ti alloy, and stainless steel (SUS304) were implanted in rat soft tissues for 6 months. The chemical states of the component elements contained in the tissues surrounding those metallic implants were analyzed by fluorescence X-ray absorption line structure (XAFS). Titanium oxide and a nickel aquo complex, which Would be Caused by the erosion of Ti and Ni, were detected in the Surrounding tissues. The concentrations of Ti and Ni in the tissues were 1-3 and 300 ppm, respectively. Thus, the dissolved conditions and concentrations of those practical metallic materials in vivo were successfully confirmed.