Starch granule was extracted from grain amaranth. Then hydrophobic modified starch granule (OSAS) was prepared by modifying starch granule with octenyl succinic anhydride. The structure of OSAS was characterized by FT-IR and XRD diffraction pattern. The hydrophobic property of the modified starch granules increased with the increasing of degree of substitution （DS）. Pickering emulsion was prepared by using liquid paraffin as the oil phase and starch granules as the sole emulsifier. When the V(oil):V(water) was 1:1, OSAS granule with DS of 0.089 concentration was above 0.5wt%, the stable emulsion could be formed. The size of droplets decreased and the stability of emulsions enhanced with the increasing of OSAS granule concentration.