Tibet is a very important biodiversity hot spot in China and the diatom flora of this region has drawn a lot of attention. Diatom samples were collected from several places across Tibet. During research on the biodiversity of diatoms from Tibet, one Achnanthidium species showed unique features compared with other known taxa. It has linear-lanceolate valves with rounded apices, tear-drop shaped proximal raphe ends and ?-shaped distal raphe ends. The most distinctive character of this species, however, is the shape of areolae; since this species has nearly round external areolar openings on the valve face but more typical slit-like areolae present on the mantle. Here we describe it as new to science as Achnanthidium tibeticum Y. Liu & Kociolek. We compare this new species with other, similar taxa within the genus.