A hemoglobin concentration-determining article comprising a water-impermeable support having integrally provided thereon, in sequence, a hydrophilic binder layer and a porous spreading layer which has a hydrophilic surface and in which the surface of the internal voids or the interior is hydrophilic and water-insoluble, said porous spreading layer being constituted so that an aqueous sample applied thereto can be spread and incorporated therein in a substantially definite volume per unit area.