Disclosed is a multilayered assay element in which the influence by the bilirubin contained in the sample fluid is substantially eliminated. The assay element of the present invention contains a bilirubin-trapping agent of the formula(A).sub.x (B).sub.y (C).sub.z [I](wherein A represents a monomer unit having a copolymerizable unsaturated double bond and a quaternary ammonium salt, B represents a monomer unit having a copolymerizable unsaturated double bond, C represents a monomer unit having at least two copolymerizable unsaturated double bonds and x, y and z represents the number mol % of 100-10, 90-0 and 10-0, respectively) which bilirubin-trapping agent is incorporated in a region which is upper than the reagent layer.