Amastra sericea is a species of air-breathing land snail, a terrestrial pulmonate gastropod mollusc in the family Amastridae.
The length of the shell attains 17 mm, its diameter 9.3 mm
The shell is imperforate, dextral, ovate-conic, and solid, with a surface characterized by coarse striation and minute granulate decussation from spiral striae, giving it a silky texture. Its coloration is deep brown, with a spire that is convexly conic and rather acute.
The shell comprises nearly six convex whorls, paler at the sutures. The body whorl constitutes two-fifths of the total length and is whitish around the columella. The columella features a short, compressed, and oblique lamina.
The aperture is oblique and elliptical. The peristome is simple and unexpanded, with the right margin forming a nearly semicircular curve and connecting angularly to the calloused columella.
This rare species is endemic to Hawaii, occurring on Oahu island.