Raman spectra of hydroxyapatite have been successfully obtained at temperatures up to 1200 degrees C for the first time by using a new system of ultraviolet (UV) Raman spectroscopy. With increasing temperature, the intensity of a band ascribed to the stretching vibration of the OH ion continuously decreased. The total intensity of bands in the wavenumber range of 3300-3800 cm(-1) did not change significantly up to about 800 degrees C, whereas they decreased at temperatures higher than about 800 degrees C. This result is interpreted as producing oxy-hydroxyapatite due to dehydration of hydroxyapatite over 800 degrees C. The withdrawal of water is accompanied by the creation of defects. This consideration is strongly supported by results of thermodynamic calculations and the line width of the Raman band.