Aconitum sikkimensis, a new species from Sikkim in the Indian Eastern Himalaya, is described and illustrated in this article. A. hookeri is morphologically closest species to the new species and it resembles in colour of the flower and the shape of the lateral sepals. However, it differs in plant height (A. sikkimensis being taller than A. hookeri), the shape of leaf and degree of dissection in the lamina, number of bracts and their shape and size, length of petiole, semi-orbicular upper sepal (vs. obliquely erect), distinctly curved, pubescent petals (vs. straight, glabrous petals) having spathulate lips (vs. obovate), and well-developed staminal pilose hairs and teeth (vs. non-developed, glabrous). Based on population data, the species was assigned the threat status of ‘Critically Endangered’ following IUCN criteria.