There is provided a polishing composition, containing abrasive grains and an acid represented either by R2—R1—SO3H (wherein R1 is a linear alkylene or hydroxyalkylene group having 1 to 4 carbon atoms, and R2 is a hydroxy group, a carboxy group, or a sulfonic acid group when R1 is the linear alkylene group, or R2 is a carboxy group or a hydroxymethyl group when R1 is the linear hydroxyalkylene group), or by C6H5—R3 (wherein R3 is a sulfonic acid group or a phosphonic acid group). The acid contained in the polishing composition is preferably isethionic acid or benzenesulfonic acid. The polishing composition is mainly used in the application of polishing silicon oxide materials including glass substrates for hard disks, synthetic quartz substrates for photomasks, and low-dielectric-constant films such as silicon dioxide films, BPSG films, PSG films, FSG films, and organosiloxane films of semiconductor devices.