Provided is a polishing composition containing at least aluminum oxide abrasive grains and water, and having a pH of 8.5 or higher. The aluminum oxide abrasive grains have a specific surface area of 20 m2/g or less. It is preferable for the aluminum oxide abrasive grains to have an average secondary particle size of 0.1 μm or more and 20 μm or less. The polishing composition is used for polishing hard and brittle materials having a Vickers hardness of 1,500 Hv or higher, such as sapphire, silicon carbide, and gallium nitride.