High purity TiO2 (rutile) single crystals were grown using the floating zone process by applying oxygen pressures of 0.3, 0.4 0.5, and 0.8 MPa, respectively. All of the as-grown single crystals were dark blue and transparent, and differed only slightly from their appearance by observation of the naked eye. Crystals grown under high oxygen pressure had just a few low-angle grain boundaries, except for the periphery of the crystal, compared to the rutile crystals grown under ambient oxygen pressure. In particular, a sin.-le crystal grown under an oxygen pressure of 0.5 MPa contains no low-angle grain boundaries, indicating that it can be used for optical devices. (C) 2002 Elsevier Science B.V. All rights reserved.