A new species of Trigastrotheca Cameron, 1906 from Doi Phu Kha National Park, Nan province, Thailand is described and illustrated based on a female specimen collected by light trapping, bringing the total number of Trigastrotheca species known from Thailand to three; T. doiphukhaensis Raweearamwong, Quicke Butcher, sp. nov., T. pariyanonthae Quicke Butcher, 2017, and T. sureeratae Quicke Butcher, 2017. The new species differs markedly in coloration from other Thai species and is most similar to T. tridentata (Enderlein) from which it is differentiated. A checklist to the 14 species known of Trigastrotheca with their distributions is provided.
Keywords: Hymenoptera, Braconidae, Braconinae, Trigastrotheca, new species, Thailand.