NiTa2O6 single crystals with trirutile structure were successfully grown by a floating zone (FZ) method. The as-grown crystals were black and opaque. After annealing in air, the crystals were pale-green and transparent. The interference figure observed with a polarizing microscope demonstrated that the grown crystals had little stress birefringence. The refractive indices for ordinary and extraordinary rays were 2.29 and 2.44 under white light, respectively, and the birefringence was 0.15. NiTa2O6 had strong absorption spectra in the wave length ranges of 300-500, 650-900 and 1100-1600 nm.