By comparing the infrared stretching bands of OH - bonds in Ti-doped sapphire samples with the infrared bands of OH - bonds in undoped sapphire samples,it is demonstrated definitely that in Ti-doped sapphire only a band 3309 cm-1 is close relationship with Ti ions,the other bands such as 3232 cm-1,3183 cm-1 have no relation with Ti ions. The OH-bonds which cause the band 3309 cm-1 must have adjacent Ti4+ ions. In undoped sapphire and ruby,the OH - bonds which cause the band 3278 cm-1 must have adjacent chromium ions. We suggest that the band is due to a stretching absorption of a interstitial OH - ion adjacent to a Cr2+-Cr4+ pair