Schistidium leptoneurum is described as a new species from King George Island and Deception Island in the South Shetland Islands archipelago in West Antarctica. It clearly belongs to sect. Conferta on account of the presence of the distinct basal marginal border in the vegetative leaves. The new species differs from all other local species of the genus Schistidium in having very narrow and weak costae which are 35–40 μm wide, bistratose throughout and not or scarcely convex on the dorsal side, and those in the perichaetial leaves end far below the apices. Moreover, S. leptoneurum has a well-developed peristome and its vegetative leaves are epilose and shorter than 1.3 mm, making it the smallest species of the genus in the Antarctic.