To provide an ultraviolet absorber for ink jet recording sheets which can keep good printing characteristics even after long-time storage and exhibits high resolution and ink absorption capability without damaging the resolution of a printer.

This ultraviolet absorber is a copolymer which is obtained by polymerizing a monomer mixture essentially comprising (a) 20-80 mass% at least one ultraviolet-absorbing monomer selected from among benzophenone- based ultraviolet-absorbing monomers and benzotriazole-based ultraviolet- absorbing monomers and (b) 80-20 mass% vinyl monomer copolymerizable with monomer (a).