To provide a protein microarray slide capable of reducing a fluorescent background, and a holder for the slide.

This protein microarray slide has first and second main surfaces on the side opposite to the slide, and one or more of opening parts for passing the slide from the first main surface to the second main surface, and one or more of membranes mounted on the one main surface of the slide over the one or more opening parts, and has abilities of both washing background fluorescence in an active membrane domain and for reducing it, the membrane is fabricated of a nitrocellulose, nylon or PVDF. The each opening part can be used to allow a washing solution that passed through the membrane, the fluorescent background is reduced with removal thereof, together with contaminants (nondeposited materials, such as a protein or an antibody, a dye staff and a salt) from the slide, and the each opening part exhibits a fluorescence lower than that of the membrane laid on the slide, since there is no slide material and no adhesive of increasing the background fluorescence at all.