Charmon thailandensis sp. nov. from Thailand is described and illustrated based on a female specimen from Doi Phu Kha National Park, Nan Province, Thailand. The new species is distinguished from apparently closely-related species of Charmon Haliday, 1833, based on both morphology and DNA sequence (barcode) data. Morphologically it appears to be near to C. extensor (L., 1758) but DNA data suggest it is quite basal with respect to all the other sequenced species. A checklist of the 10 known species of Charmon with their known distributions is provided. The possibility that C. extensor might represent a complex of more than one species is briefly discussed.