Didymocarpus middletonii Souvann., Soulad. & Tagane, a new species of Gesneriaceae from Nam Kading National Protected Area, is described and illustrated. The new species is morphologically similar to Didymocarpus brevicalyx, D. formosus and D. puhoatensis but distinguished from the three by its fewer-flowered inflorescence, longer pedicel, and urceolate and multicellular eglandular hairy calyx. Based on the latest IUCN criteria, Didymocarpus middletonii is proposed to be Critically Endangered (CR). Our record of Didymocarpus represents a new genus record for the flora of Laos.