A polishing composition for memory hard disk containing water and silica particles, wherein the silica particles have a particle size distribution in which the relationship of a particle size (R) and a cumulative volume frequency (V) in a graph of particle size-cumulative volume frequency obtained by plotting a cumulative volume frequency (%) of the silica particles counted from a small particle size side against a particle size (nm) of the silica particles in the range of particle sizes of from 40 to 100 nm satisfy the following formula (1): V.gtoreq.0.5.times.R+40 (1), wherein the particle size is determined by observation with a transmission electron microscope (TEM). The polishing composition of the present invention can be even more suitably used for the manufacture of a substrate for precision parts such as substrates for memory hard disks.