A pressure-sensitive adhesive layer of pressure-sensitive adhesive sheet is formed by using: a pressure-sensitive adhesive composition comprising (A) a polyrotaxane having a linear-chain molecule passing through opening portions of at least two cyclic molecules, the cyclic molecules having a reactive group, the polyrotaxane having blocking groups at both ends of the linear-chain molecule, and (B) a pressure-sensitive adhesive polymer having two or more functional groups capable of reacting with the reactive group; or, a pressure-sensitive adhesive composition comprising (A) a polyrotaxane having a linear-chain molecule passing through opening portions of at least two cyclic molecules, the cyclic molecules having a reactive group, the polyrotaxane having blocking groups at both ends of the linear-chain molecule, (B′) a pressure-sensitive adhesive polymer having two or more reactive groups, and (C) a compound having two or more functional groups capable of reacting with the reactive group of the polyrotaxane (A) and the reactive groups of the polymer (B′). As a result there can be provided a pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer excellent in flexibility and having high gel fraction and durability, and a pressure-sensitive adhesive composition that constitutes the pressure-sensitive adhesive layer.