A new genus and species of mycotrophic orchid (Orchidaceae), Kalimantanorchis nagamasui Tsukaya, M. Nakajima et H. Okada, from Betung Kerihun National Park, West Kalimantan, Borneo, Indonesia, is described and illustrated. Kalimantanorchis resembles the genus Tropidia Lindl. in flower and stem morphology, namely, mycotrophic habit, branching stem, nonresupinate flowers with a saccate cymbiform lip bearing two longitudinal ridges along the margins, broadly triangular rostellum, acute, triangular anther cap, and winged or three-lobed column. It differs, however, in having a tuberous root system, pure ivory-white flower coloration and four pollinia. BLAST analyses based on DNA sequences of the chloroplast matK pseudogene and ITS of the nuclear ribosomal DNA also suggest that the closest genus is Tropidia Lindl., but the similarity is low and a molecular phylogenetic analysis did not support it to be a member of Tropidia, confirming the idea that this is an undescribed genus.