A new species of Lejeunea Lib., Lejeunea liromobana sp. nov., is described from West Siang district in Arunachal Pradesh, Eastern Himalaya, India. The species is characterized by large first tooth of leaf lobule, (1–) 2–3 cells long, (1–) 2–3 cells wide at base, 1–2 cells uniseriate at apex, prominent second tooth forming a hump, occasionally unicellular; small underleaves with dentate margins; keel of male bracts not winged; perianth beak 2–3 (–4) cells long, 4–5 cells wide at base, cells elongated, arranged spirally.