The genus Besseria Robineau-Desvoidy, 1830 with 15 described species (Tachinidae: Phasiinae) is distributed in the Palaearctic, Nearctic, and Afrotropical Regions. A new species, Besseria macrocerca sp. nov., is described from the western and southern regions of Iran. This species is diagnosed and illustrated based on both male and female specimens, with particular emphasis on distinctive morphological characters and male terminalia, notably the elongated cerci. An updated key to the Palaearctic