An aqueous dispersion for chemical mechanical polishing that is hard to putrefy, scarcely causes scratches, causes only small dishing and is suitable for used in a micro isolating step or a planarizing step of an inter layer dielectric in production of semiconductor devices, which dispersion comprises ceria particles, a preservative composed of a compound having a heterocyclic structure containing a nitrogen atom and a sulfur atom in the ring, such as an isothiazolone compound, and an organic component such as organic abrasive grains composed of resin particles, a dispersing agent composed of a water-soluble polymer having a specific molecular weight or the like, a surfactant and/or an organic acid or a salt thereof contained in an aqueous medium, wherein the ceria particles, preservative and organic component are contained in proportions of 0.1 to 20% by mass, 0.001 to 0.2% by mass and 0.1 to 30% by mass, respectively, when the total proportion of the aqueous medium, ceria particles, preservative and organic component is 100% by mass, and wherein the pH of this aqueous dispersion can be kept in a neutral range.