To polish the surface of an SiO2 insulating film or the like at a high speed without flaws by a method in which cerium oxide abrasive particle which contains primary cerium oxide powder, whose grain size is prescribed by the observation with a transmission electron microscope, at a prescribed ratio is dispersed into dispersion medium to contain abrasive slurry, and the surface of the insulating film is polished with the above abrasive slurry.

Cerium oxide particle is prepared through a low-temperature burning process so as to be kept low in crystallinity as far as possible, and cerium oxide abrasive particle which contains 90% or above primary particle, whose grain size ranges from 10-100nm by the observation with a transmission electron microscope, is dispersed into medium to obtain abrasive slurry, and the surface of an SiO2 insulating film can be polished at a high speed without flaws by the use of the above abrasive slurry.