Rutile single crystals were grown at 48 degrees to the c-axis by the floating-zone method. Under a low oxygen partial pressure (a CO2 stream), which was effective to grow high-quality rutile crystals in the case of the c-axis growth, the formation of low-angle grain boundaries could not be suppressed in a pure rutile crystal grown at an angle of 48 degrees to the c-axis. Even in an oxygen stream, the addition of a small amount of ZrO2 or Al2O3 and a higher growth rate were effective to reduce the number of low-angle grain boundaries in the growth of rutile crystals inclined at 48 degrees to the c-axis. In particular, completely grain boundary free rutile crystals were grown with the addition of 1.0 at% ZrO2 at a growth rate of 10 mm/h. The extinction ratio at any point of a Savart plate made of the Zr-doped rutile single crystal was at least 50 dB.