The North Qilian Mountain suture zone is a typical early Paleozoic oceanic subduction zone, in which two blue schist zones are developed:a low-grade blue schist zone with lawsonite and a high-grade blue schist zone with eclogites. Ardennite-(As), a rare kind of silicate mineral, was found in the high-pressure metamorphic Mn-rich silica rocks in the high-grade blue schist zone containing eclogites in the North Qilian Mountain. This is the first discovery of ardennite-(As) in China. Detailed mineralogical studies were carried out by means of optical microscopy, scanning electron microscopy, electron probe microscopy, Raman spectroscopy and transmission electron microscopy. According to the results obtained, the density of ardennite-(As) is 3.69~3.75 g/cm³ and the hardness is 6~7; ardennite-(As) crystals are biaxial (+) and have perfect cleavage in (010), pleochroism is strong from pale yellow to golden yellow, usually associated with quartz, piemontite, glaucophane, phengite and hematite; the main components of ardennite-(As) are Si, Al, Mn, it is rich in As, and contains a small amount of F, V, P; in Raman spectrum; ardennite-(As) shows many characteristic peaks, probably indicating the presence of arsenate, vanadium, MnO and SiO₃ bonds; in the crystal structure, ardennite-(As) is orthorhombic, the space group is Pnmm, and the crystal axis parameters are a=8.934 Å, b=5.817 Å, c=19.005 Å. These mineralogical features can be used as the basis for the identification and study of ardennite-(As).