The moth-fly genus Horaiella Tonnoir is reported for the first time from Thailand. Numerous adult specimens were collected in Malaise-trap samples from Khao Yai National Park, central Thailand, including males and females of a new species, Horaiella iota Curler. Genitalic characters of the male confirm that the Khao Yai specimens represent a new species. A description and a brief discussion of bionomics and comparison with other known species of Horaiella are given.