A new species, Frullania tibetica Mamontov & J. J. Atwood, is described and illustrated from Tibet, China. The species is morphologically similar to F. parvistipula Steph. in its slender leafy shoots, caducous and broadly ovate dorsal lobes, consistently inflated and galeate lobules, and obcuneate underleaves with toothed lateral margins. The new species differs in its more parallel lobule position and unequally sized lobule mouth valves on well-developed shoots, broader styli, irregularly repand gynoecial lobes, lack of gemmae on the leaf margins, and perianths with a densely tuberculate and spinose ornamentation. Based on the combination of its size, presumptively dioicous sexuality, lobe, lobule, and underleaf morphology, terminal position of the gynoecia on the stem, and trigonous, conspicuously armed perianths, F. tibetica is referable to Frullania Raddi subg. Trachycolea Spruce sect. Trachycolea (Spruce) Grolle.