The present invention relates to a polishing composition containing an aqueous medium and silica particles, wherein the silica particles in the polishing composition has a zeta potential of from -15 to 40 mV; a method for manufacturing a substrate including the step of polishing a substrate to be polished with a polishing composition containing an aqueous medium and silica particles, wherein the silica particles in the polishing composition has a zeta potential of from -15 to 40 mV; and a method for reducing scratches on a substrate to be polished with a polishing composition containing an aqueous medium and silica particles, including the step of adjusting a zeta potential of silica particles in the polishing composition to -15 to 40 mV. The polishing composition can be favorably used in polishing the substrate for precision parts, including substrates for magnetic recording media such as magnetic discs, optical discs and opto-magnetic discs; photomask substrates; optical lenses; optical mirrors; optical prisms; semiconductor substrates; and the like.