Disclosed is a polishing composition that contains at least abrasive grains, an oxidizing agent having a redox potential equal to or greater than 1.8 V at a pH for application of polishing, and water. The abrasive grains are preferably composed of at least one substance selected from among silicon oxide, aluminum oxide, cerium oxide, zirconium oxide, titanium oxide, manganese oxide, silicon carbide, and silicon nitride. The oxidizing agent is preferably composed of at least one substance selected from among sodium persulfate, potassium persulfate, and ammonium persulfate. The polishing composition preferably has a pH equal to or less than 3.