POLISHING COMPOSITION

PROBLEM TO BE SOLVED: To provide a polishing composition used in polishing an object to be polished formed of a substrate material for optical devices, a substrate material for power devices, or a compound semiconductor material with high polishing speed.SOLUTION: The polishing composition contains at least abrasive grains and water and is used in polishing the object to be polished formed of the substrate material for optical devices, the substrate material for power devices, or the compound semiconductor material. The abrasive grains have a zeta potential satisfying the relationship X×Y≤0, where X [mV] represents the zeta potential of the abrasive grains measured in the polishing composition and Y [mV] represents the zeta potential of the object to be polished measured during polishing using the polishing composition. The abrasive grains are preferably of aluminum oxide, silicon oxide, zirconium oxide, diamond, or silicon carbide. The object to be polished is preferably of sapphire, gallium nitride, silicon carbide, gallium arsenide, indium arsenide, or indium phosphide.