A method of double-side polishing an object, the method comprising the steps of: holding the object to be polished held by a holding hole of the object to be polished of a holding tool of the object to be polished between a polishing pad stuck to a lower rotary platen and a polishing pad stuck to an upper rotary platen; discharging a polishing composition; and rotating the polishing pads while pressing both the surfaces of the object to be polished, wherein the object to be polished is a silicon wafer, characterized in that: the polishing composition comprises abrasives, a water-soluble polymer and a salt, wherein the average primary particle diameter of the abrasives is 30 nm or larger, the water-soluble polymer is any one of a cellulose derivative, a starch derivative, a polymer containing an oxyalkylene unit, a polymer containing a nitrogen atom, or a vinylalcohol polymer, the salt comprises potassium carbonate; and the method satisfying either the following formula or, wherein fitting of the polishing composition to the polishing pad is defined as Wp, fitting of the polishing composition to the object to be polished is defined as Ww, and fitting of the polishing composition to the holding tool of the object to be polished is defined as Wc: Wp ≥ Wc Ww ≥ Wc ≥ Wp holding the object to be polished held by a holding hole of the object to be polished of a holding tool of the object to be polished between a polishing pad stuck to a lower rotary platen and a polishing pad stuck to an upper rotary platen; discharging a polishing composition; and rotating the polishing pads while pressing both the surfaces of the object to be polished, wherein the object to be polished is a silicon wafer, characterized in that: the polishing composition comprises abrasives, a water-soluble polymer and a salt, wherein the average primary particle diameter of the abrasives is 30 nm or larger, the water-soluble polymer is any one of a cellulose derivative, a starch derivative, a polymer containing an oxyalkylene unit, a polymer containing a nitrogen atom, or a vinylalcohol polymer, the salt comprises potassium carbonate; and the method satisfying either the following formula or, wherein fitting of the polishing composition to the polishing pad is defined as Wp, fitting of the polishing composition to the object to be polished is defined as Ww, and fitting of the polishing composition to the holding tool of the object to be polished is defined as Wc: Wp ≥ Wc Ww ≥ Wc ≥ Wp the polishing composition comprises abrasives, a water-soluble polymer and a salt, wherein the average primary particle diameter of the abrasives is 30 nm or larger, the water-soluble polymer is any one of a cellulose derivative, a starch derivative, a polymer containing an oxyalkylene unit, a polymer containing a nitrogen atom, or a vinylalcohol polymer, the salt comprises potassium carbonate; and the method satisfying either the following formula or, wherein fitting of the polishing composition to the polishing pad is defined as Wp, fitting of the polishing composition to the object to be polished is defined as Ww, and fitting of the polishing composition to the holding tool of the object to be polished is defined as Wc: Wp ≥ Wc Ww ≥ Wc ≥ Wp