Aristolochia assamica D. Borah & T.V. Do (Aristolochiaceae), a new species from the East Himalayas (NE India) is described and illustrated. It has purplish to greenish terete stems, brownish ovate-lanceolate bracteoles with a short stalk at base and acuminate apex, cymes with 2–15 flowers, fasciculate, on extremely short inflorescence axes, a sessile utricle, creamy-white to greenish-yellow perianth with a brownish patch on its throat, a 1-lobed limb, oblong linear with a twisted cauda, and a 6-lobed gynostemium. According to these morphological characteristics, A. assamica should be placed in Aristolochia subgenus Aristolochia series Aristolochia. A detailed description, phenology, distribution and ecology as well as comparison with four morphologically closely similar species is presented. In addition, a key to the Indian species of Aristolochia subgenus Aristolochia section Aristolochia is provided.