A polishing composition comprising: Abrasives; and a water-soluble polymer, wherein the abrasives are silica, the abrasives have an average secondary particle size of 10 nm or more and 150 nm or less, the abrasives have an average primary particle size of 10 nm or more and 30 nm or less, the water-soluble polymer contains one selected from a copolymer containing polyvinyl pyrrolidone in a part of the structure or a polymer having polyoxyalkylene structure, a weight average molecular weight of the water-soluble polymer is 1000 or more and 1000000 or less, a content of the water-soluble polymer is 0.0001% by mass or more and 1.0% by mass or less, the polishing composition further contains a basic compound selected from hydroxides or salts of alkali metals or alkaline-earth metals, quaternary ammonium hydroxides or salts thereof, ammonia or amine, a content of the basic compound in the polishing composition is 0.0001% by mass or more and 1.0% by mass or less, and the water-soluble polymer satisfies following two conditions and: Condition: in a first standard solution containing silica having an average primary particle size of 35 nm, the water-soluble polymer, ammonia, and water, in which a concentration of the silica is 0.48% by mass, a concentration of the water-soluble polymer is 0.0125% by mass, and a pH is 10.0, an adsorption ratio defined as a ratio of an amount of the water-soluble polymer adsorbed to the silica to a total amount of the water-soluble polymer contained in the first standard solution is 10% or more; and Condition: in a second standard solution containing silica having an average primary particle size of 35 nm, the water-soluble polymer, ammonia, and water, in which the concentration of the silica is 0.48% by mass, the concentration of the water-soluble polymer is 0.0125% by mass, and the pH is 10.4, the adsorption ratio defined as a ratio of the amount of the water-soluble polymer adsorbed to the silica to the total amount of the water-soluble polymer contained in the second standard solution is 65% or less. Abrasives; and a water-soluble polymer, wherein the abrasives are silica, the abrasives have an average secondary particle size of 10 nm or more and 150 nm or less, the abrasives have an average primary particle size of 10 nm or more and 30 nm or less, the water-soluble polymer contains one selected from a copolymer containing polyvinyl pyrrolidone in a part of the structure or a polymer having polyoxyalkylene structure, a weight average molecular weight of the water-soluble polymer is 1000 or more and 1000000 or less, a content of the water-soluble polymer is 0.0001% by mass or more and 1.0% by mass or less, the polishing composition further contains a basic compound selected from hydroxides or salts of alkali metals or alkaline-earth metals, quaternary ammonium hydroxides or salts thereof, ammonia or amine, a content of the basic compound in the polishing composition is 0.0001% by mass or more and 1.0% by mass or less, and the water-soluble polymer satisfies following two conditions and: Condition: in a first standard solution containing silica having an average primary particle size of 35 nm, the water-soluble polymer, ammonia, and water, in which a concentration of the silica is 0.48% by mass, a concentration of the water-soluble polymer is 0.0125% by mass, and a pH is 10.0, an adsorption ratio defined as a ratio of an amount of the water-soluble polymer adsorbed to the silica to a total amount of the water-soluble polymer contained in the first standard solution is 10% or more; and Condition: in a second standard solution containing silica having an average primary particle size of 35 nm, the water-soluble polymer, ammonia, and water, in which the concentration of the silica is 0.48% by mass, the concentration of the water-soluble polymer is 0.0125% by mass, and the pH is 10.4, the adsorption ratio defined as a ratio of the amount of the water-soluble polymer adsorbed to the silica to the total amount of the water-soluble polymer contained in the second standard solution is 65% or less. Condition: in a first standard solution containing silica having an average primary particle size of 35 nm, the water-soluble polymer, ammonia, and water, in which a concentration of the silica is 0.48% by mass, a concentration of the water-soluble polymer is 0.0125% by mass, and a pH is 10.0, an adsorption ratio defined as a ratio of an amount of the water-soluble polymer adsorbed to the silica to a total amount of the water-soluble polymer contained in the first standard solution is 10% or more; and Condition: in a second standard solution containing silica having an average primary particle size of 35 nm, the water-soluble polymer, ammonia, and water, in which the concentration of the silica is 0.48% by mass, the concentration of the water-soluble polymer is 0.0125% by mass, and the pH is 10.4, the adsorption ratio defined as a ratio of the amount of the water-soluble polymer adsorbed to the silica to the total amount of the water-soluble polymer contained in the second standard solution is 65% or less.