Ba8Ga16Ge30 clathrate material has being intensely investigated as a candidate of promising thermoelectric materials. In this work, Ba8Ga16+xSbxGe30-2x (x=0,1) single crystals have been synthesized by the Ga flux method, using high purity elemental Ba, Sb, Ga, and Ge as starting materials. Powder X-ray diffraction, Scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy and Raman spectroscopy were used to characterize the single crystals. Seebeck coefficient of the crystals was measured from 300 to 800 K. The result indicates that the crystals are p-type semiconductor, which is different from the crystals synthesized by the Czochralski method. The Seebeck coefficient almost does not change after doping Sb in the whole temperature measured and it is in the range of 200 to 300μV/K.