Thismia submucronata is described and illustrated as a new species from Thailand. The new species is characterized by 1) vermiform roots, 2) inner perianth lobes forming a convex mitre with a mucro together with three foveae at apex, 3) the inner surface of perianth tube possessing an irregularly reticulate surface without transverse bars, 4) the presence of papillate hairs at the annulus surface and the outer surface of stamen filaments, and 5) the stamens positioned almost at apex of annulus. Morphological description, illustrations of the new species and a comparison with the related species are presented.