A polishing composition of the present invention is to be used for polishing an object including a portion containing a high-mobility material and a portion containing a silicon material. The polishing composition comprises odd-shaped abrasive grains and an oxidizing agent having a standard electrode of 0.3 V or more, and preferably further contains a salt, such as an ammonium salt. The pH of the polishing composition is 1 or more and 6 or less, or 8 or more and 14 or less. The average degree of association of the abrasive grains, obtained by dividing the value of the average secondary particle diameter of the abrasive grains by the value of the average primary particle diameter of the abrasive grains, is preferably 1.6 or more.