A polishing composition of the present invention contains abrasive grains each having a surface with protrusions. Parts of the abrasive grains have larger particle diameters than the volume-based average particle diameter of the abrasive grains, and the average of values respectively obtained by dividing a height of each protrusion on the surface of each abrasive grain belonging to the parts of the abrasive grains by the width of a base portion of the same protrusion is 0.170 or more. Protrusions on the surfaces of abrasive grains belonging to the parts of the abrasive grains that have larger particle diameters than the volume-based average particle diameter of the abrasive grains have an average height of 3.5 nm or more. The polishing composition has a content of an organic alkali of 100 mmol or less per kilogram of the abrasive grains in the polishing composition.