A polishing composition for magnetic disk substrates to be used for memory hard disks, which comprises: (a) water; (b) at least one phosphate. compound selected from the group consisting of a phosphate ester of ethoxylated alkylalcohol and a phosphate ester of ethoxylated arylalcohol; (c) at least one polishing accelerator selected from the group consisting of an inorganic acid and an organic acid, and their salts, other than the phosphate compound of component (b); (d) at least one abrasive selected from the group consisting of aluminum oxide, silicon dioxide, cerium oxide, zirconium oxide, titanium oxide, silicon nitride and manganese dioxide.