The invention provides an industrially advantageous method for the production of hydroxyalkylated polyrotaxanes. The method of producing hydroxyalkylated polyrotaxane includes reacting a polyrotaxane with a cyclic ether represented by Formula (1) in the presence of water and an organic base, wherein the polyrotaxane includes hydroxyl group-containing cyclic molecules, a linear molecule threaded through the cyclic molecules to form a clathrate, and blocking groups at both ends of the linear molecule to prevent the separation of the cyclic molecules from the linear molecule.