Disclosed is an immunochromatographic test strip by which the influences by the interfering substances in the immunochromatography method, contained in test samples, are reduced, so that it enables to accurately and specifically measure a test substance in a test sample irrespective of the amount of the test sample supplied to the assay, and to provide an immunochromatography method using the immunochromatographic test strip. The immunochromatographic test strip includes, in the order from upstream, a sample pad, a labeled substance region, a detection region and an absorption band, wherein a polymer(s) in which hydrophobic cyclic monomer(s) having an ionic functional group(s) is/are polymerized is impregnated at a region(s) upstream of the labeled substance region.