Abstract: The present invention discloses an immunochromatographic assay strip, and an assay device using the same. The assay strip includes a sample pad for receiving a liquid phase sample, a porous membrane pad having at least one reaction zone including a detecting substance to react with an analyte in the liquid phase sample, and a transparent plastic backing for supporting the sample pad and the porous membrane pad. The immunochromatographic assay device comprises the assay strip; an upper case including with a result observation window formed on the corresponding position of the reaction zone of the assay strip, and a sample receving hole formed on the corresponding position of the sample pad; and a lower case to be combined with the upper case, wherein the transparent backing of the assay strip is disposed between the upper case and the lower case to face the observation window of the upper case.