A polishing composition comprising an abrasive, an acid and/or a salt thereof, and water, wherein copper (Cu) is contained in an amount of 1 mg or less per kg of the polishing composition; a process for reducing a surface defect of a substrate comprising applying to a substrate or a polishing pad a polishing composition comprising an abrasive, an acid and/or a salt thereof, and water, wherein copper (Cu) is contained in an amount of 1 mg or less per kg of the polishing composition fed to the substrate or the polishing pad; and a process for manufacturing a substrate comprising a polishing step comprising applying to a substrate or a polishing pad the above polishing composition. The polishing composition of the present invention is used for polishing a substrate for precision parts such as substrates for magnetic recording media such as magnetic disks, optical disks, opto-magnetic disks, and the like; photomask substrates, optical lenses, optical mirrors, optical prisms and semiconductor substrates, concretely polishing a substrate for memory hard disks, and especially finish polishing.
