PROBLEM TO BE SOLVED: To provide a deformed silica sol suitable as abrasive materials such as an abrasive material for CMP and the like.SOLUTION: In the deformed silica sol, the ratio (r/r', hereinafter called the "association ratio") of the average particle diameter (r) measured by a dynamic light scattering method to the equivalent sphere conversion particle diameter (r') calculated from the average specific surface area measured by a nitrogen adsorption method is within the range of 1.2-10, the equivalent sphere conversion particle diameter (r') is within the range of 5-200 nm, the specific surface area is within the range of 13-550 m/g, fine deformed silica particles having uneven shapes are dispersed in a solvent and the ratios of Ca and Mg (in terms of oxides) contained in the fine deformed silica particles to SiOare 1,000 ppm or less respectively.