A new species, Begonia pasighatensis D.Borah, Taram & Wahlsteen (Begoniaceae) is described and illustrated. It is easily distinguished from all other species in the section Platycentrum by its swollen, spherical ovary with two wings reduced to ridges and a long, pointing upper wing. The new species belongs to Begonia section Platycentrum and is distributed in southern Arunachal Pradesh in East India. We also report a finding of the rare species Begonia scintillans in the Namdapha National Park. This species is similar to B. thomsonii but differs in number of styles and color of the indumentum. Both species are illustrated by photographs and a distribution map is provided.